The Algerian army on Saturday carried out a "final assault" on al Qaida-linked gunmen holed up in a desert gas plant, killing 11 of the Islamists after they took the lives of seven foreign hostages.

"It is over now, the assault is over, and the military are inside the plant clearing it of mines," a local source familiar with the operation told Reuters.

The state oil and gas company, Sonatrach, said the militants who attacked the plant on Wednesday and took a large number of hostages had booby-trapped the gas complex with explosives.

The exact death toll among the gunmen and the foreign and Algerian workers at the plant near the town of In Amenas close to the Libyan border remained unclear.

Earlier on Saturday, Algerian special forces found 15 burned bodies at the plant. Efforts were underway to identify the bodies, the source told Reuters, and it was not clear how they had died.

Sixteen foreign hostages were freed on Saturday, a source close to the crisis said. They included two Americans, two Germans and one Portuguese.

Britain said fewer than 10 of its nationals at the plant were unaccounted for.

The attack on the plant swiftly turned into the biggest international hostage crises in decades, pushing Saharan militancy to the top of the global agenda.

Reports earlier put the number of hostages killed at between 12 to 30, with many foreigners still unaccounted for, among them Norwegians, Japanese, Britons and Americans.

The U.S. State Department said on Friday one American, Frederick Buttaccio, had died but gave no further details. The French defense minister said he understood there were no more French workers among the hostages.

Two Norwegians were released overnight, leaving six unaccounted for, while Romania said three of its nationals had been freed. A number of Japanese engineering workers were still unaccounted for.

Scores of Westerners and hundreds of Algerian workers were inside the heavily fortified compound when it was seized before dawn on Wednesday by Islamist fighters who said they wanted a halt to a French military operation in neighboring Mali.

Hundreds escaped on Thursday when the army launched its operation, but many hostages were killed.

Multinational insurgency

Algerian commanders said they moved in on Thursday about 30 hours after the siege began, because the gunmen had demanded to be allowed to take their captives abroad.

A French hostage employed by a French catering company said he had hidden in his room for 40 hours under the bed before he was rescued by Algerian troops, relying on Algerian employees to smuggle him food with a password.

"I put boards up pretty much all round," Alexandre Berceaux told Europe 1 radio. "I didn't know how long I was going to stay there ... I was afraid. I could see myself already ending up in a pine box."

The captors said their attack was a response to the French military offensive in neighboring Mali. However, some U.S. and European officials say the elaborate raid probably required too much planning to have been organized from scratch in the single week since France first launched its strikes.

Paris says the incident proves its decision to fight Islamists in neighboring Mali was necessary.

Security in the half-dozen countries around the Sahara desert has long been a preoccupation of the West. Smugglers and militants have earned millions in ransom from kidnappings.

The most powerful Islamist groups operating in the Sahara were severely weakened by Algeria's secularist military in a civil war in the 1990s. But in the past two years the regional wing of Al-Qaida gained fighters and arms as a result of the civil war in Libya, when arsenals were looted from Muammar Gadhafi's army.

Al-Qaida-linked fighters, many with roots in Algeria and Libya, took control of northern Mali last year, prompting the French intervention in that poor African former colony.

The apparent ease with which the fighters swooped in from the dunes to take control of an important energy facility, which produces some 10 percent of the natural gas on which Algeria depends for its export income, has raised questions over the value of outwardly tough Algerian security measures.

Algerian officials said the attackers may have had inside help from among the hundreds of Algerians employed at the site.

U.S. Defense Secretary Leon Panetta said those responsible would be hunted down: "Terrorists should be on notice that they will find no sanctuary, no refuge, not in Algeria, not in North Africa, not anywhere. ... Those who would wantonly attack our country and our people will have no place to hide."