ALGIERS (REUTERS) - A total of 37 foreign workers died at an Algerian desert gas plant, and seven are still missing after a hostage crisis coordinated by a Canadian, Algerian Prime Minister Abdelmalek Sellal said on Monday.

Mr Sellal also said 29 Islamists were killed in the siege, which Algerian forces ended by storming the plant, and three were captured alive.

Earlier, an Algerian security source told Reuters that documents found on the bodies of two militants identified them as Canadians, as special forces scoured the plant following Saturday's bloody end to the siege.

"A Canadian was among the militants. He was coordinating the attack," Mr Sellal told a news conference, adding that the raiders threatened to blow up the gas installation.

The Canadian's name was given only as Chedad.

In Ottawa, Canada's foreign affairs department said it was seeking information, but referred to the possible involvement of only one Canadian.

American, British, French, Japanese, Norwegian, Filipino and Romanian workers are dead or missing after the attack, for which veteran Islamist fighter Mokhtar Belmokhtar has claimed responsibility on behalf of Al-Qaeda.

The jihadists planned the attack two months ago in neighbouring Mali, where French forces began fighting Islamists this month, Mr Sellal added.

In Tokyo, Prime Minister Shinzo Abe told a news conference he received information that seven Japanese were killed, and the fate of three more was still unknown.

Six Filipinos died and four were wounded, a government spokesman in Manila said.

Norwegian International Development Minister Heikki Holmaas said his stepfather, Mr Tore Bech, was among the missing and presumed dead. Mr Bech was a manager at the site for the Norwegian energy company Statoil.

Mr Sellal said initially the raiders in Algeria tried to hijack a bus carrying foreign workers to a nearby airport and take them hostage.

"They started firing at the bus and received a severe response from the soldiers guarding the bus," he said. "They failed to achieve their objective, which was to kidnap foreign workers from the bus."

He said special forces and army units were deployed against the militants, who planted explosives in the gas plant with a view to blowing up the facility.

One group of militants tried to escape in some vehicles, each of which also was carrying three or four foreign workers, some of whom had explosives attached to their bodies.

After what he called a "fierce response from the armed forces", the raiders' vehicles crashed or exploded, and one of their leaders was among those killed.

Mr Sellal said the jihadists who staged the attack last Wednesday crossed into the country from neighbouring Libya.

An Algerian newspaper said they arrived in cars painted in the colours of state energy company Sonatrach but registered in Libya, a country awash with arms since Muammar Gaddafi's fall in 2011.

The raid has exposed the vulnerability of multinational-run oil and gas installations in an important producing region and pushed the growing threat from Islamist militant groups in the Sahara to a prominent position in the West's security agenda.

Algerian President Abdelaziz Bouteflika has ordered an investigation into how security forces failed to prevent the attack, the daily El Khabar said.

Algerian Tahar Ben Cheneb, leader of a group called the Movement of Islamic Youth in the South who was killed on the first day of the assault, had been based in Libya where he married a local woman two months ago, it said.

Belmokhtar, a one-eyed jihadist who fought in Afghanistan and Algeria's civil war of the 1990s when the secular government fought Islamists, tied the desert attack to France's intervention across the Sahara against Islamist rebels in Mali.

"We in Al-Qaeda announce this blessed operation," he said in a video, according to Sahara Media, a regional website. About 40 attackers participated in the raid, he said, roughly matching the government's figures for fighters killed and captured.

Belmokhtar demanded an end to French air strikes against Islamist fighters in neighbouring Mali. These began five days before the fighters swooped before dawn and seized a plant that produces 10 per cent of Algeria's natural gas exports.

US and European officials doubt such a complex raid could have been organised quickly enough to have been conceived as a direct response to the French military intervention.

However, the French action could have triggered an operation that had already been planned.

The group behind the raid, the Mulathameen Brigade, threatened to carry out more such attacks if Western powers did not end what it called an assault on Muslims in Mali, according to the SITE service, which monitors militant statements.

In a statement published by the Mauritania-based Nouakchott News Agency, the hostage takers said they offered talks about freeing the captives, but the Algerian authorities was determined to use military force. Mr Sellal blamed the raiders for the collapse of negotiations.

The siege turned bloody on Thursday when the Algerian army opened fire, saying fighters were trying to escape with their prisoners. Survivors said Algerian forces blasted several trucks in a convoy carrying both hostages and their captors.

Nearly 700 Algerian workers and more than 100 foreigners escaped, mainly on Thursday when the fighters were driven from the residential barracks. Some captors remained holed up in the industrial complex until Saturday when they were overrun.

The bloodshed has strained Algeria's relations with its Western allies, some of which have complained about being left in the dark while the decision to storm the compound was being taken.

Nevertheless, Britain and France both defended the military action by Algeria, the strongest military power in the Sahara and an ally the West needs in combating the militants.

Among other foreigners confirmed dead by their home countries were three Britons, one American and two Romanians.

The missing include five Norwegians, three Britons and a British resident. An Algerian security source said at least one Frenchman was also among the dead.

The raid on the plant, which was home to expatriate workers from Britain's BP , Norway's Statoil, Japanese engineering firm JGC and others, exposed the vulnerability of multinational oil operations in the Sahara.

However, Algeria is determined to press on with its energy industry. Oil Minister Youcef Yousfi visited the site and said physical damage was minor, state news service APSE reported. The plant would start up again in two days, he said.

Algeria, scarred by the civil war with Islamist insurgents in the 1990s which claimed 200,000 lives, insisted from the start of the crisis there would be no negotiation in the face of terrorism. France especially needs close cooperation from Algeria to crush Islamist rebels in northern Mali.