The captors are demanding a prisoner swap and an end to French military action in Mali.
The Al-Qaeda-linked gunmen, cited by Mauritania’s ANI news agency, said they still held seven foreigners at the site deep in the Sahara desert near the border with Libya. An Algerian security official put their number at 10.
Abdul Rahman, the spiritual leader of the radical Jamaa Islamiya group, was convicted in 1995 for his role in a 1993 attack on the World Trade Centre in New York City, in which six people were killed.
He is serving a life sentence for the attack in which hundreds more people were injured when a truck bomb was detonated in the building’s garage.
Abdul Rahman, known as the “blind sheikh,” was also convicted of plotting to bomb other New York targets including the United Nations and a plan to assassinate ousted Egyptian president Hosni Mubarak.
Mubarak’s successor, President Mohamed Morsi, said earlier this month he will urge US President Barack Obama to free Abdul Rahman, during a visit he is due to make to the United States later before the end of March.
“This is an extremely difficult and dangerous situation,” US Secretary of State Hillary Clinton said in Washington at a joint news conference with an equally concerned Japanese Foreign Minister Fumio Kishida.
“The United States extends our condolences to all the families who have lost loved ones in this brutal assault and we remain deeply concerned about those who remain in danger.”
International criticism of the haste with which Algeria launched a dramatic military assault to rescue the hostages has been mounting, after an Algerian security official said it had left dead 12 hostages and 18 kidnappers.
“The government of Japan has been requesting the government of Algeria to place the utmost priority on ensuring the safety and the lives of the hostages,” Kishida told the joint news conference.
French Foreign Minister Laurent Fabius said a Frenchman had been killed in the operation. A US official said an American military transport had begun to help evacuate survivors, but gave no estimate of the number of US hostages.
A security official said troops were trying to reach a “peaceful” end to the hostage crisis, before “neutralising the terrorist group that is holed up in the plant and freeing a group of hostages still being held there.”
The kidnappers said they were still holding three Belgians, two Americans, one Japanese and a Briton, although Belgium said there was no indication any of its nationals were being held.
More workers remain unaccounted for, and the fate of at least 10 Japanese nationals and eight Norwegian hostages still unknown.
US Secretary of State Hillary Clinton urged Algeria to show “utmost care” to preserve the lives of the hostages and offered condolences for those killed.
“Utmost care must be taken to preserve innocent life,” Clinton told reporters alongside Kishida. US Defence Secretary Leon Panetta said the United States was “working around the clock” to secure the safe return of Americans, as Washington ruled out talks for a hostage swap.
Some of those who escaped said explosives had been wrapped around their necks and others said they hid, petrified, wherever they could.
Alexandre Berceaux of French catering firm CSI said he took cover in his room before troops freed him.
“I was under the bed and I put boards everywhere just in case,” Berceaux said. “I had a bit of food, a bit to drink. I didn’t know how long it would last.”
Algerian forces launched their rescue bid on Thursday, a day after kidnappers seized the plant to avenge what they said was Algiers’ support for French military action in neighbouring Mali. British Prime Minister Cameron said he was “disappointed” not to have been told in advance about the rescue bid at the field, operated jointly by British energy giant BP, Norway’s Statoil and Sonatrach of Algeria.
France said two of its nationals had returned safely but it had no word on two more. Vienna said one Austrian had been released.
A Northern Ireland man, Stephen McFaul, escaped. His brother said he fled when the convoy he was in came under army fire.
The gunmen group known as “Signatories in Blood” want an end to the French intervention in Mali and to exchange American hostages for US-held prisoners,
ANI quoted sources close to their leader, Mokhtar Belmokhtar, as saying.
ANI said Belmokhtar, a veteran Algerian Islamist with Al-Qaeda ties who has claimed responsibility for the attack, had proposed Paris and Algiers negotiate “an end to the war being waged by France in Azawad” (northern Mali).
He also proposed exchanging US hostages held by his group for Egyptian Omar Abdul Rahman and Pakistani Aafiah Siddiqui, jailed in the United States on charges of terrorist links.
“The United States does not negotiate with terrorists,” State Department spokeswoman Victoria Nuland said when asked about the proposal.
Clinton spoke to Algerian Prime Minister Abdelmalek Sellal to try to coordinate efforts on the “extremely fluid” hostage crisis, she added.