About 32 foreign hostages are still unaccounted for in the standoff with Islamist militants at an Algerian gas plant, according to the Algerian state news service.

In statements Friday, London-based BP, Norway’s Statoil and other companies said many hostages had escaped or were rescued in the military operation launched by Algerian troops at dawn Thursday. The plant is jointly run by BP, Statoil and the Algerian state energy company, Sonatrach

Reports are starting to emerge from freed hostages, some of whom said that explosives were strapped to their chests and that they had to hide behind furniture for days to avoid the attackers.

One British hostage who managed to contact his wife soon after being taken told her: "I'm sat here at my desk with Semtex (high explosive) strapped to my chest. The local army have already tried and failed to storm the plant and they've said that if that happens again they are going to kill us all," the Daily Mail reported. The report said that 12 Britons are among the casualties.

Régis Arnoux, chief executive of Catering International Services (CIS), which employs some 150 Algerian staff at the plant, told French radio that all of his employees were safe and that French ex-patriots were in the process of being sent home.

Arnoux gave this account in an interview on I-Tele TV:

"The French expatriate collaborators who were on the site are all safe and sound. All of them have been evacuated, or all of them are on route to being evacuated. [One hostage,] Alexandre Berceaux, is on route to France."
"The information that I have is that the Algerian army won't make any new assaults. They have encircled the whole perimeter so as to search the whole location, which is vast, to verify that not one terrorist is remaining in the sector."

Berceaux said he hid behind some planks of wood in a room away from other foreign hostages, according to Reuters, and that he survived thanks to food brought by Algerian colleagues.

"I stayed hidden for nearly 40 hours in my bedroom, under the bed," Berceaux told Europe 1 radio after his release, saying that he had believed he was going to be killed and that he was still in shock.

"When the military came to get me, I did not know whether it was over," he said. "They arrived with colleagues (Algerians who worked with him); otherwise I would never have opened the door."

One unidentified Algerian worker told Algerian television that he had been petrified during the hostage situation.

“The operation happened at 5:30 in the morning… it was a horrific thing to be in,” the man said. “We were 300 or 400 Algerians from the company, and others who were doing services in the factory. They took all the hostages -- foreigners, as well as locals. Then they booby-trapped the area. We were all in a terrifying situation, waiting for a sign from the military."

It also appeared as though the Algerian hostages were separated from foreign workers, according to a New York Times interview with an Algerian man who worked on the site and escaped on Thursday afternoon. That man also said that the attackers had shot several foreign hostages, execution-style.

The attackers told Algerians that they were their “brothers,” the man said...

At one point, he said, the fighters shot a European man in the back in the presence of other hostages. It was not clear why he had been shot, the man said, and he did not know if the man was alive or dead. He claimed that there had been several executions, but that he had not been present for them.

According a man identified by France Info radio as a freed Algerian engineer, the attack came suddenly, and the attackers knew what they were looking for: foreigners.

“All of a sudden, gunshots, explosions. We didn’t know what was going on,” the man said. “They plunged us into darkness. They cut off the electricity. They broke open the doors of our rooms, calling out, ‘We’re looking for expats. Algerians, you can leave.’”

The man said that the attackers had north African accents and that he believed they were from Algeria or Libya. He said they were about 30 to 35 years old. According to ANI, the attack was carried out by a group calling itself “Signatories in Blood,” an arm of the Masked Brigade, an Islamist group led by Mokhtar Belmokhtar, a one-eyed, 40-year-old Algerian Islamist who has been known to engage in kidnapping for ransom and smuggling.

Below is a compilation of video interviews with some of the freed hostages: (Parts are in Arabic, English starts at about 2:30)

British Prime Minister David Cameron told parliament Friday that rescue attempts are still underway in parts of the compound, .

“This is a large and complex site, and they are still pursuing terrorists and possibly some of the hostages,” Cameron said.

According to the Daily Mail, fierce gun battles erupted as Algerian troops moved in to the complex Thursday. One eyewitness described a scene of carnage, saying: "There were bodies all over the ground."  Another spoke of Algerian forces firing at "anything that moved," the Daily Mail report said.

Michael Birnbaum and Eliza Mackintosh contributed to this report