The kidnappers were equipped with AK-47 rifles and put explosive-laden vests on some hostages, a U.S. State Department official said.

Some escaped by disguising themselves, according to Regis Arnoux, who runs a catering firm at the site and had spoken with some of his 150 employees who were freed. He said they all were traumatized.

Some Algerian hostages were free to walk around the site but not to leave, Arnoux said. Still, a number of them escaped, he said.

As the Algerian military launched its operation Thursday, the militants moved some hostages, according to one survivor's account.

With plastic explosives strapped around their necks, these captives were blindfolded and gagged before being loaded into five Jeeps, according to the brother of former hostage Stephen McFaul.

McFaul, with the explosives still around his neck, escaped after the vehicle he was in -- one of several targeted by Algerian fighters -- crashed, his brother said from Belfast, Northern Ireland.

"I haven't seen my mother move as fast in all my life, and my mother smile as much, hugging each other," Brian McFaul said upon his family hearing his brother was safe. "... You couldn't describe the feeling."

McFaul said the other four Jeeps were "wiped out" in an explosion, and his brother believed the hostages inside did not survive.

Nations mobilize to help citizens caught up in crisis

U.S. Defense Secretary Leon Panetta, speaking in London, said the United States was working round the clock to ensure the safe return of its citizens.

Those freed include some Americans, while other U.S. nationals were unaccounted for, U.S. officials said.

The United States was evacuating 10 to 20 people caught up in the crisis, a U.S. defense official told CNN on Friday. They were to be taken to U.S. facilities in Europe, where their condition would be assessed, the official said.

Britain has sent trauma experts and consular affairs officers who can issue emergency passports to a location about 450 kilometers (280 miles) away from the plant, a Foreign Office official said, so they'll be "as close" as possible to the scene.

BP, which helps operate the gas field, said Friday that a "small number of BP employees" were unaccounted for. The same held for some workers with Statoil, though nine others with the company -- including five who escaped -- were safe. Four Norwegians and a Canadian with that oil firm were in an airport hotel in Bergen, Norway, after being taken from Algeria, Statoil spokeswoman Sissel Rinde said.

Both BP and Statoil -- two of the foreign companies with In Amenas operations -- were pulling their personnel out of Algeria, which is Africa's largest natural gas producer and a major supplier of natural gas to Europe.

BP said it had flown 11 of its employees and several hundred staffers from other companies out of the North African country Thursday and was planning another flight Friday.

Mark Cobb, a Texan who has a LinkedIn profile identifying him as general manager for a BP joint venture out of In Amenas, said he had escaped on the first day and was safe.

A U.S. military C-130 plane flew 12 people who were wounded in the ordeal out of Algeria on Friday, a U.S. defense official said. None of them were Americans, though efforts continue to evacuate freed Americans.

Three workers for a Japanese engineering company that was working on the site have been contacted and are safe, said Takeshi Endo, a senior manager for JGC Corp. But the company had not been able to contact 14 others, he said.

France's foreign ministry said that, in addition to one death, three of its citizens were rescued.