North Korean leader Kim Jong Un speaks during a ceremony to award party and state commendations to nuclear scientists, technicians, soldier-builders, workers and officials for their contribution to what North Korea said was a succesful hydrogen bomb test, at the meeting hall of the Central Committee of the Workers' Party of Korea (WPK) in this undated photo released by North Korea's Korean Central News Agency (KCNA) on January 13, 2016. REUTERS/KCNA

SEOUL (Reuters) - North Korea on Saturday called for the conclusion of a peace treaty with the United States and a halt to U.S. military exercises with South Korea to end its nuclear tests.

The isolated state has long sought a peace treaty with the United States, as well as an end to the exercises by South Korea and the United States, which has about 28,500 troops based in South Korea.

"Still valid are all proposals for preserving peace and stability on the peninsula and in Northeast Asia including the ones for ceasing our nuclear test and the conclusion of a peace treaty in return for U.S. halt to joint military exercises," North Korea's official KCNA news agency cited a spokesman for the country's foreign ministry as saying early on Saturday.

Asked if the United States would consider a halt to joint exercises, U.S. State Department spokesman John Kirby said it had alliance commitments to South Korea.

"We are going to continue to make sure the alliance is ready in all respects to act in defense of the South Korean people and the security of the peninsula," he told a regular news briefing.

Asked earlier this week about North Korea's call for a peace treaty, the State Department reiterated its position that it remained open to dialogue with North Korea but said "the onus is on North Korea to take meaningful actions toward denuclearization and refrain from provocations."

The two Koreas remain in a technical state of war since their 1950-53 conflict ended in a truce, not a peace treaty.

North Korea said on Jan. 6 it had tested a hydrogen bomb, provoking condemnation from its neighbors and the United States.

Experts have expressed doubt that the North's fourth nuclear test was of a hydrogen bomb, as the blast was roughly the same size as that from its previous test, of a less powerful atomic bomb, in 2013.

Pyongyang is under U.N. sanctions for its nuclear and missile programs.

(Reporting by Tony Munroe in Seoul; additional reporting by David Brunnstrom in Washington, editing by Andrew Roche and Tom Brown)

Aleppo (Syria) (AFP) - Pro-regime fighters are preparing to launch a major assault to recapture Syria's second city Aleppo, a security source in the northern province told AFP.

"Through its operations, the army is trying to broaden its security zone around the city," and prevent the rebels from receiving supplies and reinforcements from the suburbs, the source said.

Once Syria's commercial hub, Aleppo city is now divided between government control in the west and rebel control in the east.

The broader province is split as well, with the Islamic State jihadist group largely in the east, and rebel groups and Syria's Al-Qaeda affiliate, Al-Nusra Front, in the west.

But with backing from Russian air strikes and foreign fighters, Syria's armed forces are slowly advancing south and southeast of the city.

"This will be the biggest military operation in Syria since the beginning of the war," one commander with pro-government forces told AFP.

He said loyalist forces were fighting on seven fronts around the city of Aleppo in a bid to cut off rebel supplies and isolate the city's east.

According to Syria analyst Fabrice Balanche, rebel fighters entrenched in the city have set up "serious defence lines" against attacks from the western neighbourhoods.

Russia’s military buildup shows no signs of slowing. Moscow recently ordered 50 twin-engine Sukhoi Su-35S multirole fighters to bolster the country’s air force.

The new order, first reported by TASS Defense, is valued to be somewhere between $788 million and $1.4 billion, according to trade press reports. The Kremlin ordered 48 of the aircraft in 2009; most of the aircraft have now been delivered, with some spotted late last year flying near the disputed Kuril Islands.

Related: Putin Flexes His Muscles in the Pacific with the New Su-35 Fighter

Sukhoi also recently inked a $2 billion agreement with China for 24 Su-35S jets and reached a deal to produce another dozen for Indonesia. Last week the company signed an agreement with Algeria for 12 Sukhoi Su-32 tactical bombers, concluding eight years of negotiations.

The lucrative contracts have helped boost Russia’s economy, which has been walloped in recent years by economic sanctions over the nation’s actions in Ukraine and the dramatic tumble in the price of oil.

The deals, particularly the one with China, also allows Russian President Vladimir Putin to poke his thumb in the eye of the U.S. and its NATO allies at a time of great global tensions, including those in the South China Sea where Beijing is creating man-made islands in an effort to expand its military footprint in Asia.

As for the Su-35 itself, the jet is an updated version of the Su-27 (NATO code name: Flanker), a workhorse of the Russian Air Force. Many analysts compare the Su-35 to the F/A-18 Super Hornet made by Boeing.

The Su-35 can carry guide air-to-air and air-to-surface missiles, among other arms. The updated plane has a new integrated control system that improves the fighter's handling and maneuverability, better engines and improved stealth radar, according to Sukhoi’s website. The jet’s thrust vectoring engines enable it to make unusual maneuvers while flying (see the video below).

Related: Stealth Wars: China Rolls Out a New J-20, Another Knockoff Fighter

The planes cost around $65 million each, similar to the F/A-18, but far less than the Lockheed Martin-produced F-22 Raptor, with a price tag of $150 million, or the F-35 Joint Strike Fighter, which costs around $100 million or more depending on the variant.

Hadalat (Jordanie) (AFP) - Abdelhadi Zarara, six children in tow, juggles with his emotions as he crosses into Jordan, as thousands of other Syrian refugees wait in no-man's land hoping their turn will come.

Zarara, 39, says "there was nothing left for me in Syria," where his wife was killed a few months ago in a regime bombardment that also destroyed the family home in southern Daraa province.

According to Jordanian authorities the number of Syrians stuck along its desert border with Syria jumped from a few hundred three months ago to 16,000 by the start of January.

They are fleeing the nearly five-year war, leaving behind death and devastation in the hope of making a new life in Jordan or beyond, with many eying Europe as their final destination.

But only 50 to 100 will be lucky enough to cross into Jordan each day, according to the army and aid agencies.

The kingdom says it is hosting 1.4 million Syrian refugees -- equal to 20 percent of Jordan's population and more than twice as many as the 600,000 figure given by the UN refugee agency UNHCR.

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A Syrian woman receives medical attention after crossing into Jordan, at the Hadalat border crossing …

During the first two years of the Syrian conflict, there were 45 crossing points along the 378-kilometre (235-mile) frontier.

Now just two remain open, in rocky, hard to access areas devoid of water, shade or vegetation, according to UNHCR.

One of them is at Hadalat, 500 kilometres northeast of the capital Amman, while the other is at Rokbane, 70 kilometres further east.

Around 1,300 Syrians are stuck in Hadalat, while in Rokbane 15,000 are trapped in dire conditions, said General Saber Al-Mahayra, the head of Jordan's border guards unit.

- 'Weeding' out jihadists -

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Jordan says it is hosting 1.4 million Syrian refugees -- equal to 20 percent of its population and m …

Intensified fighting in Syria, including the launch of Russian air raids in September in support of Damascus, has sparked a fresh wave of refugees seeking safety in Jordan, Mahayra said.

Zarara and his children arrived in Hadalat in October.

"There weren't many people around and we had nothing to protect us from the cold and the rain," he said.

The Jordanian army gave them food and blankets but it was only several weeks later that UNHCR provided shelter in the form of tents, he said.

In early December, UNHCR and New York-based Human Rights Watch issued separate pleas urging Jordanian authorities to allow all the refugees to enter the desert kingdom, warning of deteriorating conditions.

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Intensified fighting in Syria, including the launch of Russian air raids in September in support of …

But Jordan has stood its ground, allowing only a trickle at a time in and insisting that it must screen newcomers to ensure they are genuine refugees and not armed jihadists seeking to infiltrate the country.

"Our security is above everything else," said Mahayra.

After the conflict erupted in March 2011, Syrians who sought refugee in Jordan were mostly from the southern Daraa province across the border, he said.

But recent newcomers have travelled from as far as Raqa, the self-declared capital of the Islamic State group in northern Syria.

"In a bid to weed out jihadist infiltrators, the army is carrying out meticulous controls at the border," Mahayra said, adding that two suspected jihadists who tried to pass for refugees were recently arrested.

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Jordan is allowing in only a trickle at a time and insisting it must screen newcomers to ensure they …

- Eyeing Europe -

Riyadh, 23, was one of the lucky few who entered Jordan on Thursday after "83 painful days" trapped in no-man's land, he said as he dusted off his clothes caked in sand.

He too came from Daraa, after losing hope that he would be able to finish his last year at university there.

"Security conditions won't allow it," he said.

Hassad, who crossed into Jordan with his wife and five children, said he had to pay people smugglers 100,000 Syrian pounds ($440, 400 euros) for each member of his family.

"I am hoping for a better future for my children," he said, adding that Jordan would only be a stepping stone towards their new life.

"Our goal is to travel to Europe, soon I hope," he said.

Army trucks lined up on the Jordanian side of the Hadalat crossing to transport the newcomers to a reception centre where refugees would undergo medical checks and further security controls.

After that they will be taken to one of two refugee camps in northern Jordan -- Zaatari or Azraq -- which are run jointly by the Jordanian authorities and the UN.

The camps are home to about 20 percent of all Syrian refugees in the kingdom.