Smoke rises from Al-Safsaf in Homs August 3, 2012. REUTERS/Shaam News Network/Handout

ALEPPO, Syria (Reuters) - Syrian forces stormed the last rebel stronghold in the capital Damascus in tanks and armored vehicles on Friday and blasted artillery at rebels in Aleppo, where the United Nations said the army was preparing a massive assault.

The violence came within hours of former United Nations Secretary-General Kofi Annan quitting as international peace envoy for Syria, underlining the impotence of mediation efforts in the 17-month-old uprising against President Bashar al-Assad.

A senior U.N. official said a long-expected army onslaught to take Aleppo, Syria's largest city and economic hub, was imminent following a buildup of army reinforcements. The fighting in Aleppo has focused on the Salaheddine district, seen as a gateway to the city for the Syrian army.

Rebels poured into Aleppo in July after being largely driven from the capital, Damascus, where they had launched an offensive that coincided with a bomb blast that killed four top security officials. The fighting in Syria's two main cities has intensified the conflict over the past three weeks.

Rebels told Reuters journalists inside Aleppo on Friday that they had captured a large police station after days of clashes. Rebel commander Abu Zaher said fighters had taken several police officers prisoner and seized weapons and ammunition.

Other rebels said heavy fighting was taking place in Saleheddine, the main battleground district, where they estimated 20 civilians had been killed. They say 50 of their fighters have been killed there in the last several days.

U.N. Secretary-General Ban Ki-moon said "acts of brutality" reported in Aleppo could be crimes against humanity. Both sides have accused each other of carrying out summary executions of prisoners in the city.

U.N. member states voted overwhelmingly to condemn the Syrian government at a special session of the General Assembly that Western diplomats said highlighted the isolation of Assad supporters Russia and China.

DAMASCUS TO ALEPPO

In the capital, Syrian troops entered Damascus's southern district of Tadamon with dozens of tanks and armored vehicles in a push to win back the last rebel stronghold there, a witness and activists said.

Activists said most of the district was under the control of government forces by early Friday evening. The army had been trying to enter Tadamon for more than a week but was pushed back by fierce resistance from the rebels.

An activist said the troops had executed several people after entering the district. The account could not be confirmed.

"Thousands of soldiers have entered the neighborhood, they are conducting house-to-house raids," a resident, who did not want to be identified for security reasons, said by telephone.

The fighting spread to Aleppo from Damascus after the bomb attack on Assad's security headquarters in the capital on July 18, which killed four of the president's senior aides and encouraged rebels to step up hostilities.

The Syrian army has reinforced its positions in and around Aleppo over the past two weeks, while conducting daily artillery and aerial bombardments of rebel forces in the city.

"The focus two weeks ago was on Damascus. The focus is now on Aleppo, where there has been a considerable buildup of military means, and where we have reason to believe that the main battle is about to start," Herve Ladsous, the Under-Secretary-General for Peacekeeping Operations, said in New York.

HELICOPTER BOMBARDMENT

Annan resigned on Thursday, complaining of "finger-pointing" at the United Nations while the bloodshed in Syria went on. His mission, centered on a peace plan and a ceasefire that never took hold, had looked increasingly futile amid escalating violence.

In an article published on the Financial Times website, Annan said Russia, China and Iran "must take concerted efforts to persuade Syria's leadership to change course and embrace a political transition."

"It is clear that President Bashar al-Assad must leave office," Annan said.

However, in a sign that Russia is not yet ready to abandon support for its ally, Moscow hosted a Syrian oil official and promised to send gasoline in return for crude that Syria is having difficulty selling because of sanctions.

"We are ready to deliver all of our oil and receive what we need in gasoline and diesel," Qadri Jamil, Syria's deputy prime minister for economic affairs, told journalists in Moscow.

At the United Nations, the 193-nation General Assembly approved a Saudi-drafted resolution that expressed "grave concern" at the escalation of violence in Syria, with 133 votes in favor, 12 against and 31 abstentions. Russia and China were among those opposed.

The resolution has the assembly "deploring the failure of the Security Council to agree on measures to ensure the compliance of Syrian authorities with its decisions."

Syrian Ambassador Bashar Ja'afari complained that the meeting was "another piece of theater," adding that the "resolution will have no impact whatsoever."

KEY CITY

Aleppo, with its 2.5 million inhabitants, is a prize that could determine the outcome of a war the Syrian opposition says has already cost 18,000 lives.

Internet and telephone networks in Aleppo were mostly cut for the third day, hampering attempts by rebels to coordinate and forcing them to use couriers to deliver orders. Soldiers were launching rockets at insurgents from an infantry school north of Aleppo.

Areas around the city are divided, with some villages loyal to Assad and others favoring the opposition. Police and soldiers were setting up mobile checkpoints on some main roads leading into the city from the north.

There are increasing signs of quarrelling among rebel factions and between fighters and the population.

"The Free Syrian Army is causing us headaches now," said Abu Ahmed, a local official who works with journalists in the Syrian town of Azaz, near the Turkish border.

"If they don't like the actions of a person they tie him up, beat him and arrest him. Personality differences between brigade members are being settled using kidnappings and force. They are self-righteous and we are not happy about it," he told Reuters.

Elsewhere in the country, opposition activists said Syrian forces had killed at least 50 people during clashes with rebels in the central city of Hama on Thursday, while a helicopter bombardment killed 16 rebels near the southern town of Deraa.

In Damascus, at least 20 people were killed on Thursday when security forces fired three mortar rounds at a Palestinian camp that is home to 100,000 refugees, medical sources said. Palestinian leaders in the West Bank and Gaza condemned the attack.

(Additional reporting Dominic Evans and Mariam Karouny in Beirut, Gabriela Baczynska in Moscow, Tom Miles in Geneva, Khaled Yacoub Oweis in Amman, Sui-Lee Wee in Beijing and Louis Charbonneau at the United Nations; Writing by Giles Elgood; Editing by Peter Graff, Claudia Parsons, Doina Chiacu)

Officials warn of crisis in northern Africa

The signs of desperation came as resilient rebels fought regime forces in the Syrian capital only two weeks after the government crushed a revolt there. The renewed battles in Damascus show that Assad's victories could be fleeting as armed opposition groups regroup and resurge.

"The fighting in Damascus today proves that this revolution cannot be extinguished," said activist Abu Qais al-Shami. "The rebels may be forced to retreat because of the regime's use of heavy weaponry but they will always come back."

Syria is thought to be burning quickly through the $17 billion in foreign reserves that the government was believed to have at the start of Assad's crackdown on a popular uprising that erupted in March 2011. The conflict has turned into a civil war, and rights activists estimate more than 19,000 people.

Deputy Prime Minister Qadri Jamil, who has led a delegation of several Cabinet ministers to Moscow over the past few days, told reporters Friday that they requested a Russian loan to replenish Syria's hard currency reserves, which have been depleted by a U.S. and European Union embargo on Syrian exports.

He said Damascus also wants to get diesel oil and other oil products from Russia in exchange for crude supplies.

"We are experiencing shortages of diesel oil and gas for heating purposes," Syrian Oil Minister Said Maza Hanidi said in Moscow. "This unfair blockade has hurt all layers of the population."

The Syrian regime has blamed sanctions for shortages that have left Syrians across the country standing in long lines to pay inflated prices for cooking gas, fuel, sugar and other staples.

Syrian officials refused to mention specific figures but said that deals with Moscow could be finalized within weeks. There was no immediate comment from the Russian government.

While the Syrian delegation was holding talks in Moscow, a squadron of Russian warships was approaching Syria's port of Tartus, the only naval base Russia has outside the former Soviet Union.

Russian news agencies reported that two of the three amphibious assault ships will call at Tartus while the third will cast anchor just outside the port.

They said that each of the three ships is carrying about 120 marines backed by armoured vehicles. It wasn't immediately clear whether some of the marines will stay to protect Tartus. Some Russian media said the marines were supposed to ensure a safe evacuation of Russian personnel and navy equipment from the base if necessary.

Russia has protected Syria from U.N. sanctions and continued to supply it with weapons throughout the conflict. The Kremlin, backed by fellow veto-wielding U.N. Security Council member China, has blocked any plans that would call on Assad to step down.

On Friday, the U.N. General Assembly overwhelmingly denounced Syria's crackdown in a symbolic effort meant to push the deadlocked Security Council and the world at large into action on stopping the civil war.

Before the vote, Secretary-General Ban Ki-Moon accused the Syrian regime of possible war crimes and drew comparisons between the failure to act in Syria with the international community's failure to protect people from past genocide in Srebrenica and Rwanda.

"The conflict in Syria is a test of everything this organization stands for," Ban said. "I do not want today's United Nations to fail that test."

Syrian Ambassador Bashar Ja'afari called the resolution's main sponsors, Saudi Arabia, Qatar and Bahrain, "despotic oligarchies."

"The draft resolution will have no impact whatsoever. It is a piece of theatre," he told reporters after the vote. And Iran's No. 2 ambassador, Eshagh Alehabib, called the resolution "one-sided."

Assad's regime stands accused of a number of massacres in which hundreds of civilians, including women and children, were killed. The Syrian government blames gunmen driven by a foreign agenda for the killings, but the U.N. and other witnesses have confirmed that at least some were carried out by pro-regime vigilante groups, known as shabiha.

But the recent emergence of videos showing summary executions committed by rebel forces — albeit on a far smaller scale than the regime's alleged atrocities — is making it more difficult for the Syrian opposition to claim the moral high ground.

With the civil war becoming increasingly vicious, chances for a diplomatic solution were fading after the resignation Thursday of Kofi Annan, the U.N.-Arab League envoy to Syria. Annan cited divisions within the Security Council preventing a united approach to stop the fighting.

The fighting continued Friday in the country's two most important cities, Aleppo and Damascus.

In Damascus, residents reported loud explosions and plumes of smoke over the southern edge of the city Friday, as frightened people stayed at home.

"The bombs are back, I have been hearing explosions all day," a resident of central Damascus told The Associated Press, asking to remain anonymous for fear of reprisals.

Government forces crushed a rebel assault on Damascus two weeks ago, but pockets of resistance remain including the southern neighbourhood of Tadamon, where most of Friday's fighting took place.

Late Friday, Syria's official news agency SANA said government forces had hunted down the remnants of the "terrorist mercenaries" — its term for the rebels — in Tadamon. It said several were killed and many others wounded.

Al-Shami and other activists said troops backed by dozens of tanks and armoured vehicles broke into Tadamon on Friday evening, forcing a fresh wave of residents spilling into nearby areas for shelter.

Many Damascus residents had earlier taken refuge in the country's largest Palestinian refugee camp, Yarmouk, where mortar shells raining down on a crowded marketplace killed 21 people late Thursday.

Nevertheless, there were signs that rebels may be planning another run on Damascus in an effort to drain the army's resources as fighting stretches into its second week in Aleppo, 350 kilometres (215 miles) to the north.

The U.N. peacekeeping chief, Herve Ladsous, warned of a major government assault on Aleppo in the coming days to retake the rebel-held neighbourhoods.

"The focus is now on Aleppo, where there has been a considerable buildup of military means," he told reporters in New York late Thursday after briefing the Security Council on his trip to Syria. "We have reason to believe that the main battle is about to start."

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Flames leap into the air as area firefighters fight a wildfire on Cemetery Road east of 120th on Friday, Aug. 3, 2012, east of Norman, Okla. A wildfire stirred by high winds sweeping through rural woodlands just south of the Oklahoma City area has set at a number of homes on fire. (AP Photo/The Oklahoman, Steve Sisney)

NOBLE, Okla. (AP) — The gusty, southerly winds that whipped wildfires through rural woodlands north and south of Oklahoma City started to die down early Saturday, but not before burning dozens of homes.

Hundreds of people were told Friday to leave their homes in at least four counties, while smoke and flames prompted authorities to close parts of Interstate 44, the main roadway between Oklahoma City and Tulsa, and two state highways. I-44 reopened late Friday night.

"A man refused to leave. From what I know, he wanted to protect his property, but your life has to be more valuable than property," Oklahoma County Sheriff John Whetsel said late Friday night.

The sheriff said at least 25 homes, a daycare center and numerous outbuildings had burned in a fire that may have been deliberately set near Luther, a town about 20 miles northeast of Oklahoma City.

Deputies were looking into reports about someone in a pickup truck who was seen throwing out newspapers that had been set on fire. By Friday night, the blaze had spread across 80 square miles, but officials said it had calmed some due to lighter winds and higher humidity.

About 40 structures were destroyed by a blaze near Tulsa. And yet another blaze destroyed at least 25 structures, including a handful of homes, after starting near Noble, about 30 miles south of Oklahoma City, and moving toward Norman, home to the University of Oklahoma.

Steve Palladino, operations chief for the Oklahoma Department of Emergency Management, said six Oklahoma National Guard helicopters will be dispatched to the fires on Saturday. Palladino said three were sent out on Friday.

"I loaded the kids up, grabbed my dogs, and it didn't even look like I had time to load the livestock, so I just got out of there," said Bo Ireland, who lives a few miles from where the Noble-area fire started. "It looked to me that, if the wind shifted even a little bit, I would be in the path of that fire. It was just too close."

There were no immediate reports of injuries or livestock losses.

Dayle Bishop said he may not have made it out of his home had a woman not knocked on his door and woken him up. Standing in a convenience store parking lot about 2 miles away from his home, he was pessimistic about its chances.

"I know it's gone," said Bishop, who works nights as a nurse. "Didn't even have time to get anything out." But he noted, "it's just stuff."

Charles Wright was with his daughter, Christina, along with their cat, at a makeshift evacuation center doubling as a staging area for fire engines, ambulances and other emergency equipment. He said law enforcement ordered them to leave their home in Norman.

"Praying for miracles. Praying for the best, that's all we can do," said Wright, who managed to pack some clothes, jewelry and legal papers before fleeing.

Ruth Hood splashed water onto two Chihuahua puppies that she grabbed along with several other animals and her children, and left as flames burned in her neighbor's yard. She said she couldn't be sure her home would survive.

"No guarantee," Hood said.

With the ongoing drought, high temperatures and gusty winds, it took little for fires to begin and spread — and there was little crews could do to fight them.

"It's difficult for the firefighters to get into the area because it's heavily wooded on either side of the smaller roads. When the winds are blowing 25 mph it just blows the embers and fireballs across the roads as if they weren't even there," said Jerry Lojka with the Oklahoma Department of Emergency Management.

At mid-afternoon Friday, the temperature in Norman hit 113 degrees, and winds were gusting at 24 mph. "I can tell you the temperatures and the wind are not helping the situation at all," said Meghan McCormick, a spokeswoman for the Cleveland County Sheriff's office.

Russell Moore, 53, who lives in the Noble area, said he was outside in his yard when a sheriff's deputy drove down the road and told people to leave. He and his son went to a shelter set up at Noble City Hall.

"About all we saw was smoke and a little bit of ash raining down from the sky," Moore said. "Everybody was piling into their vehicles and leaving as we were."

The state was monitoring 11 fires by Friday afternoon. Gov. Mary Fallin announced a statewide burn ban as the fire danger heightened. She previously had announced a state of emergency for all 77 counties due to the extreme drought.

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Associated Press writers Rochelle Hines and Sean Murphy in Oklahoma City contributed to this report.