Security forces found the bodies of 25 hostages on Sunday as they combed a desert gas plant after a deadly stand-off with Islamists, and witnesses said nine Japanese captives had been executed.

Citing security sources, Anis Rahmani of private television channel Ennahar told Agence France Presse the army discovered "the bodies of 25 hostages" as they secured the sprawling In Amenas Sahara site.

A total of three British nationals are confirmed dead in the Algerian hostage crisis and a further three, plus a British resident, are believed to be dead, Prime Minister David Cameron said on Sunday.

"I spoke to the Algerian prime minister yesterday and it is now clear that this appalling terrorist incident in Algeria is now over," he said in a statement.

U.S. President Barack Obama said Saturday that blame for deaths stemming from a hostage crisis in Algeria lay with the "terrorists" who had earlier taken foreigners captive at a remote gas plant.

The remarks were the president's first direct comments about the protracted hostage crisis. His statement was released several hours after Algerian troops stormed the gas plant to end a situation that had began four days earlier.

A Japanese engineering firm said Sunday that 10 of its Japanese and seven of its foreign workers remained unaccounted for at an Algerian gas plant seized by Islamist militants, adding the situation was "grave".

The Malaysian Foreign Ministry, quoting the firm, JGC Corp., said that two of its nationals were among the seven unaccounted for, and there was a "worrying possibility" that one of them was dead. The other three Malaysians who had been working at the plant had been confirmed safe.

The apparent leader of a commando group that took hundreds of gas workers hostage in Algeria warned in a recording broadcast Saturday that he would blow them up if the army got too close.

In the audio recording, broadcast by the Mauritanian news agency ANI, Al-Mulathameen Brigade commander Abdul Rahman al-Nigeri of Niger spoke late Thursday as the Algerian military surrounded his fighters' position at a BP oil plant deep in the Sahara desert at In Amenas.

A dramatic four-day hostage crisis at an Algerian gas plant ended in a bloodbath Saturday when Islamists executed all seven of their remaining foreign captives as troops stormed the desert complex.

Twenty-one hostages, including an unknown number of foreigners, died during the siege that began when the al-Qaida-linked gunmen attacked the facility deep in the Sahara at dawn on Wednesday, the interior ministry said.

Islamists were holding a number of foreigners hostage at a gas plant deep in the Algerian desert on Saturday, nearly 48 hours after a failed rescue attempt killed at least 12 of them, a security source said.

Al-Qaida-linked gunmen said after Thursday's rescue raid they still held seven foreigners -- three Belgians, two Americans, one Japanese and a Briton -- inside the sprawling Sahara complex in northeast Algeria near the border with Libya.

The U.N. Security Council on Friday strongly condemned the "heinous" attack and hostage-taking at an Algerian gas complex by al-Qaida linked militants.

A statement agreed by the 15-member council stressed the need to bring the al-Qaida linked attackers and their backers to justice.

Algerian special forces have freed nearly 650 hostages from Islamist gunmen at a remote gas plant near the Libyan border, but some 60 foreigners are still missing, national media said on Friday.

"Nearly 650 hostages seized in the attack carried out on Wednesday by a terrorist group... among them 573 Algerians and more than half of the 132 foreign hostages, were freed" by Algerian special forces, the APS news agency reported.

"Terrorists" who attack U.S. interests have no place to hide, Defense Secretary Leon Panetta said on Friday as fears grew for dozens of foreigners taken hostage by Islamists at a gas plant in Algeria.

"Terrorists should be on notice that they will find no sanctuary, no refuge. Not in Algeria, not in north Africa, not anywhere," Panetta said in a speech at Kings College London university.