ALGIERS, Algeria (AP) — The militants had filled five jeeps with hostages and begun to move when Algerian government attack helicopters opened up on them, leaving four in smoking ruins. The fifth vehicle crashed, allowing an Irish hostage inside to clamber out to safety with an explosive belt still strapped around his neck.

Three days into the crisis at a natural gas plant deep in the Sahara, it remained unclear how many had perished in the faceoff between Africa's most uncompromising militant group and the region's most ruthless military.

By Friday, around 100 of the 135 foreign workers on the site had been freed and 18 of an estimated 30 kidnappers had been slain, according to the Algerian government, still leaving a major hostage situation centered on the plant's main refinery.

The government said 12 workers, both foreign and Algerian, were confirmed dead. But the extremists have put the number at 35. And the government attack Thursday on the convoy — as pieced together from official, witness and news media accounts — suggested the death toll could go higher.

In Washington, U.S. officials said one American — a Texan — was known to have died.

Meanwhile, the al-Qaida-linked Masked Brigade behind the operation offered to trade two American hostages for two terrorists behind bars in the U.S., including the mastermind of the 1993 World Trade Center bombing. The U.S. rejected the deal out of hand.

"The United States does not negotiate with terrorists," declared State Department spokeswoman Victoria Nuland.

The Algerian government released few details about the continuing siege at the Ain Amenas plant, which is jointly run by BP, Norway's Statoil and Algeria's state-owned oil company. By Friday, however, the outlines of the takeover by Islamic militants were coming into focus.

The attack had been in the works for two months, a member of the Masked Brigade told an online Mauritanian news outlet that often carries al-Qaida-related announcements. The band of attackers included militants from Algeria, Mali, Egypt, Niger, Mauritania and Canada, he said.

He said militants targeted Algeria because they expected the country to support the international effort to root out extremists in neighboring Mali.

Instead of passing through Algeria's relatively well-patrolled deserts, the attackers came in from southern Libya, where there is little central government and smugglers have long reigned supreme, according to Algeria's Interior Minister Daho Ould Kabila.

He said the attackers consisted of about 30 men armed with rocket launchers and machine guns and under the direct supervision of the Masked Brigade's founder himself, Moktar Belmoktar, a hardened, one-eyed Algerian militant who has battled the Algerian government for years and has built a Saharan smuggling and kidnapping empire linked to al-Qaida.

Early Wednesday morning, they crept across the border, 60 miles (100 kilometers) from the natural gas plant, and fell on a pair of buses taking foreign workers to the airport. The buses' military escort drove off the attackers in a blaze of gunfire that sent bullets zinging over the heads of the crouching workers. A Briton and an Algerian, probably a security guard, were killed.

Frustrated, the militants turned to the vast gas complex, divided between the workers' living quarters and the refinery itself, and seized hostages, the Algerian government said.

Several of the former hostages, who arrived haggard-looking on a late-night flight into Algiers on Friday, said that the gunfire began around 5 a.m. and that the militants who stormed the living quarters almost immediately separated out the foreigners. (None of those interviewed would allow their last names to be used, fearing trouble for themselves or their families.)

Mohamed, a 37-year-old nurse, said at least five people were shot to death, their bodies still in front of the infirmary when he left Thursday night.

Chabane, who worked in the food service, said he bolted out the window and was hiding when heard the militants speaking among themselves with Libyan, Egyptian and Tunisian accents. At one point, he said, they caught a Briton.

"They threatened him until he called out in English to his friends, telling them, 'Come out, come out. They're not going to kill you. They're looking for the Americans.' A few minutes later, they blew him away," Chabane said.

The militants declared that the takeover was prompted by France's attacks on al-Qaida-linked rebels in Mali, and they demanded that the intervention end or the hostages would pay for it.

The takeover soon turned into a standoff as military units from a nearby base surrounded the complex.

On Wednesday night, Kabila, Algeria's top security official, announced that in accordance to Algeria's longstanding policy, "we reject all negotiations with the group." Despite regular elections, Algeria is run by a coterie of generals and ruling party leaders who got the country through a bloody, decade-long Islamist rebellion with brutal tactics that earned them the nickname "the eradicators."

On Thursday afternoon, Algerian military forces saw a five-jeep convoy moving from one part of the complex to another. Fearing the kidnappers were trying to make a break for it, they sent attack helicopters into action.

Irish electrician Stephen McFaul was in that convoy and made it out alive as the world exploded around him.

"Four of the jeeps were taken out and everybody in them was killed," McFaul's brother, Brian, told the Irish Times. "The jeep my brother was in crashed and my brother made break for it," with a belt of explosives strapped around his neck.

The kidnappers called the Mauritanian news service ANI to say that 35 hostages and 15 of their fighters had been killed in the bloodbath — a figure that was impossible to confirm. The kidnappers told ANI that they were just trying to consolidate hostages into a single location when the Algerians attacked.

On Friday, it became clear the Algerian forces had retaken only the living quarters. Hostages and their kidnappers remained ensconced in the refinery.

An international outcry mounted over the Algerians' handling of the crisis. Experts noted that this is how they have always dealt with terrorists.

"It's the Russian training for dealing with terrorism," said Matieu Guidere, a longtime expert on al-Qaida and Algeria. "The message is: We will terrorize the terrorists. ... This is clear. The life of hostages is nothing in the balance."

The Algerian government insisted it had to intervene to prevent a catastrophe.

"As European counterterrorism experts have emphasized, no operation to liberate hostages carried out in such exceptionally complex conditions can succeed 100 percent without some damage," a security official, speaking on condition of anonymity because he was not authorized to discuss the sensitive operation, told the state news agency.

In Washington, the Obama administration said it was trying to secure the release of Americans held by the militants. It would not say how many there were.

Secretary of State Hillary Rodham Clinton defended Algeria.

"Let's not forget: This is an act of terror," she said. "The perpetrators are the terrorists. They are the ones who have assaulted this facility, have taken hostage Algerians and others from around the world as they were going about their daily business."

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Schemm reported from Rabat. Associated Press writers Sarah DiLorenzo and Elaine Ganley in Paris and Shawn Pogatchnik in Dublin, Ireland, contributed to this report.