Faced with international outrage over the killing of hostages at a sprawling gas plant in the middle of the Sahara desert, Algeria was under pressure to bring an end to a four-day standoff with Islamist extremists that has killed at least 12 captives and left dozens unaccounted for.

The standoff has put the spotlight on militancy plaguing the region and al-Qaeda-linked groups roaming remote areas from Mali to Libya, threatening vital infrastructure and energy interests.

With little official information emerging from the Algerian government about why it is taking so long to end the operation near the Libyan border, a freed hostage described the harrowing moments of his escape today.

Ruben Andrada, 49, a Filipino civil engineer who works as one of the project management staff for the Japanese company JGC Corp, told The Associated Press that an Algerian helicopter gunship opened fire on vehicles carrying hostages and the gunmen who used them as shields.

On Thursday, about 35 hostages were loaded into seven SUVs in a convoy that included 15 militants from the housing complex, Andrada said. The militants placed "an explosive cord" around their necks and were told they would explode if they tried to run away, he said.

Later, they were being moved to the gas plant itself when the convoy was chased by army helicopters that fired on the vehicles, he said.

"When we left the compound, there was shooting all around," Andrada said. "I closed my eyes. We were going around in the desert. To me, I left it all to fate.

He later saw the blasted remains of other vehicles, and the severed leg of one of the gunmen. Another hostage who survived, an Irish man, reported seeing a severed head from one of the people in the vehicles.