Algeria: 20 hostages escape, including Americans

"It was an operation conceived well in advance — spectacular and needing a lot of preparation ... It was not at all an improvised operation," he told the Europe 1 radio. "The operation was probably already scheduled and simply getting all those people into the desert would take several days."

It is certainly the largest haul of hostages since 2003, when the radical group that later evolved into al-Qaida in North Africa snatched 32 Western tourists. This is also the first time Americans have been involved.

BP, the Norwegian company Statoil and the Algerian state oil company Sonatrach, operate the gas field. A Japanese company, JGC Corp, provides services for the facility as well.

It was not immediately possible to confirm the identities of the hostages. Ireland said a 36-year-old Irish man was among them, and Britain and the U.S. said their citizens were taken, without giving numbers. The Norwegian company Statoil said 12 of its employees were captured — nine Norwegians and three locals. Japanese media reported at least 3 Japanese among the hostages and the Malaysian government confirmed two of its citizens were taken.

British Foreign Secretary William Hague told BBC radio on Thursday that he has dispatched a team to Algeria to help at the British embassy there.

"Excuses being used by terrorists and murderers who are involved — there is no excuse for such behavior, whatever excuse they may claim," he said. "It is absolutely unacceptable, of course. It is, in this case, the cold-blooded murder of people going about their business. So there is no excuse, whether it be connected to Libya, Mali or anywhere else."

In Rome on Wednesday, U.S. Defense Secretary Leon Panetta declared that the U.S. "will take all necessary and proper steps" to deal with the attack in Algeria. He would not detail what such steps might be but condemned the action as "terrorist attack."

BP said it would not identify staff members who were taken hostage for security reasons.

"BP's overriding priority is to do all we can to ensure the safety of our staff and to support their families during this anguishing time," BP CEO Bob Dudley said in a statement. "All our efforts are focused on supporting the authorities to secure a peaceful resolution of the situation and the safe return of our colleagues and all other workers being detained."

Schemm reported from Rabat. Associated Press writers Lori Hinnant in Paris and Robert Barr in London, contributed to this report.