Some captives were strapped with explosives or used as human shields

"You are Algerians and Muslims, you have nothing to fear. We're looking for Christians, who kill our brothers in Mali and Afghanistan," the militants shouted to their Algerian hostages, as chilling accounts emerged of the siege.

The gunmen, numbering more than 30 and belonging to the "Signatories in Blood" group of Mokhtar Belmokhtar, former commander of al-Qaida in the Islamic Maghreb, launched their brazen hostage attack at the In Amenas gas plant at dawn on Wednesday.

Riad, an Algerian employee of Japan's JGC engineering firm, described how three of his Japanese colleagues were executed after the militants attacked the bus that was taking them to the airport.

"We were all terrified when we heard bursts of gunfire at 5:30 am (local time) on Wednesday, after we realized that they had just killed our Japanese colleagues, who tried to flee," he said.

The gunmen then took the passengers to the plant's residential compound, where they had seized hundreds of foreign and Algerian hostages.

"A terrorist shouted 'Open the door!' in a strong North American accent and opened fire. Two other Japanese died then and we found four other Japanese bodies in the compound", said Riad, choking with emotion.

Joseph Balmaceda, a Filipino survivor, said the militants used foreign hostages as human shields to stop Algerian troops on helicopters from attacking them with gunfire.

"Whenever government troops tried to use a helicopter to shoot at the enemy, we were used as human shields," Balmaceda told reporters after arriving back in Manila.

No official images of the attack have been released. But survivors took photos, seen by AFP, showing bodies riddled with bullets.

"They were brutally executed," said Brahim, another Algerian who escaped the ordeal, referring to some of the Japanese victims.

In the past few days, survivors have told how explosives were strapped to them. The apparent leader of the militants, Abdul Rahman al-Nigeri, confirmed he was ready to blow up the hostages at any time.

A British man was threatened into calling out to his colleagues in English: "Come out, they're not going to kill you," according to an Algerian worker named Chabene, who heard the exchange before he escaped.

"They ordered the man to yell, 'They're not going to kill you. They're looking for the Americans.' A few minutes later they blew him away."

Abdelkader, an employee of the British oil firm BP that jointly operates the plant, was at a security post with some colleagues when he saw a jeep with seven people inside smashing through the barrier and screeching to a halt.

Getting out of the vehicle, one of the militants confiscated their mobile phones and ordered them not to move.

"He said: 'We're looking for Christians, who kill our brothers in Mali and Afghanistan and plunder our resources.'"

The assailants then shot a security guard in the foot and led the group to the plant, said Abdelkader, who is in his 40s. He was freed after telling the gunmen he was a father of four.

The death toll from the siege is reportedly more than 80.

Algeria said after Saturday's assault by government forces that at least 32 extremists and 23 hostages were killed. On Sunday, Algerian bomb squads found 25 more bodies, said a security official, who spoke on condition of anonymity.

The witnesses agreed the hostage-takers were "very well informed" about the sprawling In Amenas gas complex, deep in the Algerian Sahara close to the Libyan border, which they occupied for four days.

They knew the internal procedures and the room numbers of the foreign workers. They attacked the bases of BP and JGC, the only ones where there were foreigners, said Riad. "They had accomplices on the inside."

He and his companions escaped on Thursday during an exchange of gunfire between the kidnappers and the Algerian special forces.

The Algerians fled to the buildings of the Italian firm Sarpi, which had been spared the attack. When the BP living quarters were liberated, they went to the JGC base to gather their belongings.

There they discovered the bodies of seven Islamists and a Malaysian colleague in a state of shock, hiding under the bed.

AFP-AP