ALGIERS/IN AMENAS, Algeria: Algeria said on Sunday it expected heavy hostage casualties after its troops ended a desert siege, but Western governments warned against criticising tactics used by their vital ally in the struggle with Islamists across the Sahara.

An Algerian minister acknowledged the death toll would rise, and a private television station reported that 25 bodies had been found at the gas plant near the town of In Amenas after forces staged a final assault against the Islamist hostage-takers on Saturday.

Some Western governments had expressed frustration at not being informed of the Algerian authorities' plans to storm the complex. But France, which is fighting Islamist rebels across the desert in Mali, joined Britain in playing down any suggestion the response from Algeria - the main military power in the Sahara region - had been over-hasty or heavy-handed.

"What everyone needs to know is that these terrorists who attacked this gas plant are killers who pillage, rape, plunder and kill. The situation was unbearable," French Foreign Minister Laurent Fabius said.

"It's easy to say that this or that should have been done. The Algerian authorities took a decision and the toll is very high but I am a bit bothered ... when the impression is given that the Algerians are open to question. They had to deal with terrorists," he told Europe 1 radio in an interview.

The Islamists' pre-dawn attack on Wednesday has tested Algeria's relations with the outside world, exposed the vulnerability of multinational oil operations in the Sahara and pushed Islamist radicalism in northern Africa to centre stage.

Algeria, scarred by a civil war with Islamist insurgents in the 1990s which claimed 200,000 lives, had insisted there would be no negotiation in the face of terrorism.

Prime Minister David Cameron pointed out on Sunday its record in fighting Islamists. "Of course people will ask questions about the Algerian response to these events, but I would just say that the responsibility for these deaths lies squarely with the terrorists who launched this vicious and cowardly attack," he said in a television statement.

"We should recognise all that the Algerians have done to work with us and to help and coordinate with us. I'd like to thank them for that. We should also recognise that the Algerians too have seen lives lost among their soldiers."

France especially needs close cooperation from Algeria to have a chance of crushing Islamist rebels in northern Mali. Algiers has promised to shut its porous 1,000-km border with Mali to prevent al Qaeda-linked insurgents simply melting away into its empty desert expanses and rugged mountains.

Algeria's permission for France to use its airspace, confirmed by Fabius last week, also makes it much easier to establish direct supply lines for its troops which are trying to stop the Islamist rebels from taking the whole of Mali.

Algeria's Interior Ministry had reported on Saturday that 23 hostages and 32 militants were killed during the assaults launched by Algerian special forces to end the crisis, with 107 foreign hostages and 685 Algerian hostages freed.

However, Minister of Communication Mohamed Said said this would rise when final numbers were issued in the next few hours. "I am afraid unfortunately to say that the death toll will go up," Said was quoted as saying by the official APS news agency.

Details are only slowly emerging on what happened during the siege, which marked a serious escalation of unrest in northwestern Africa.

Private Algerian television station Ennahar said on Sunday that 25 bodies had been discovered at the Tiguentourine plant, adding that the operation to clear the base would last 48 hours.

The bodies were believed to belong to hostages executed by the militants, said Ennahar TV, which is known to have good sources within Algerian security.

In London, Cameron said three British nationals had been confirmed killed, while a further three Britons plus a British resident were also believed to be dead.

One Briton had already was confirmed killed when the gunmen seized the hostages at the plant near the Libyan border, run by Norway's Statoil along with Britain's BP and Algeria's state oil company.

Said reported that the militants had six different nationalities and the operation to clear the plant of mines laid by the hostage-takers was still under way.

Believed to be among the 32 dead militants was their leader, Abdul Rahman al-Nigeri, a Nigerien close to al Qaeda-linked commander Mokhtar Belmokhtar, presumed mastermind of the raid.

One American has also been confirmed dead. Statoil said five of its workers, all Norwegian nationals, were still missing. Japanese and American workers are also unaccounted for.

On Saturday President Barack Obama said the United States was seeking a "fuller understanding" from Algerian authorities of what had happened, but added that "the blame for this tragedy rests with the terrorists who carried it out".

BP's chief executive Bob Dudley said on Saturday four of its 18 workers at the site were missing. The remaining 14 were safe.

The militant attack was one of the most audacious in recent years and almost certainly planned before French troops launched the operation in Mali this month to stem an advance by Islamist fighters.

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

Before the Interior Ministry released its provisional death toll, an Algerian security source said eight Algerians and at least seven foreigners were among the victims, including two Japanese, two Britons and a French national.

The U.S. State Department said on Friday one American, Frederick Buttaccio, had died but gave no further details.

Mauritanian news agencies identified the field commander of the group that attacked the plant as Nigeri, a fighter from one of the Arab tribes in Niger who had joined the Algerian Salafist Group for Preaching and Combat (GSPC) in early-2005.

That group eventually joined up with al Qaeda to become Al Qaeda in the Islamic Maghreb (AQIM). It and allied groups are the targets of the French military operation in Mali.

The news agencies described him as "one of the closest people" to Belmokhtar, who fought in Afghanistan and then in Algeria's civil war of the 1990s. Nigeri was known as a man for "difficult missions", having carried out attacks in Mauritania, Mali and Niger.

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 country's outwardly tough security measures.

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

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 the civil war in the 1990s. But in the past two years the regional wing of al Qaeda gained fighters and arms as a result of the civil war in Libya, when arsenals were looted from Muammar Gaddafi's army.