The Islamist militants who attacked a natural gas plant in the Sahara included two Canadians and a team of explosives experts who had memorized the layout of the sprawling complex and were ready to blow the place sky-high, Algeria's prime minister says, but officials in Ottawa have yet to confirm Canadians were involved.

Abdelmalek Sellal did not say Monday whether the Canadians were among the 29 militants killed by Algerian forces that stormed the site, or the three who were captured alive. At least 37 hostages died in the attack, with five more unaccounted for, according to Algeria.

There have been changing reports about the numbers and profiles of those involved.

Algeria's Prime Minister Abdelmalek Sellal tells reporters during a press conference in Algiers on Monday that 37 foreign hostage died during the siege at an Algerian desert gas plant last week. (Reuters)

The militants had said during the four-day standoff that their band included people from Canada.

Reuters reported that Sellal said a Canadian co-ordinated the attack, giving the militant's name only as Chedad.

The kidnappers came from Egypt, Canada, Mali, Niger, Mauritania and Tunisia, the prime minister said.

Other news reports have cited security sources as saying two Canadians were among the hostage-takers. Some of the hostages who had escaped recalled hearing at least one of the militants speaking English with a North American accent.

Ottawa seeking more information

As of Monday morning, there has been no official communication between the Algerian and Canadian governments about the identity or the nationality of any of the hostage takers, the Prime Minister's Office told CBC News.

One government source told CBC News that until Canadian officials see the proof themselves they will not confirm whether Canadians were involved in the attack.

The Canadian government said earlier Monday it's aware of reports that Canadians may have been involved in the hostage incident at the Ain Amenas natural gas plant.

'We are pursuing all appropriate channels to seek further information and are in close contact with Algerian authorities.'— Chrystiane Roy, Department of Foreign Affairs

"We are pursuing all appropriate channels to seek further information and are in close contact with Algerian authorities," foreign affairs spokeswoman Chrystiane Roy told CBC News on Monday.

"Canada condemns in the strongest possible terms this deplorable and cowardly attack and all terrorist groups which seek to create and perpetuate insecurity in the Sahel countries of West Africa."

Meanwhile, Foreign Affairs said this weekend it believes no Canadians or dual nationals were among the hostages. A permanent resident of Canada who was at the site is safe and has left Algeria.

Canadian jihadists

Ray Boisvert, former assistant director of intelligence for CSIS, said that some Canadians are known to be involved in jihadist activities.

"There are 50-plus Canadian passport holders who have either left the country — or attempted to leave the country to engage in some form of violent jihad — or some form of violent activism," Boisvert told CBC News.

The documents carried by these attackers could be stolen or forged passports, Boisvert said, and it may be difficult to get a clear picture of the incident and the people involved.

“It's usually impossible to do any forensics, whether it is recovering the body or examining any documents."

Attack planned for 2 months

The Algerian prime minister, speaking to reporters in the capital of Algiers on Monday, said a number of the hostages were found killed with a bullet to the head.

The militants wore Algerian army uniforms, and included a team of explosives experts ready to blow up the place, he said. The group "knew the facility's layout by heart," Sellal added.

"Their goal was to kidnap foreigners," the prime minister said. "They wanted to flee to Mali with the foreigners but once they were surrounded they started killing the first hostages."

The facility had 790 Algerian workers and 134 foreigners from 26 countries, he said. Algeria says 685 Algerian workers and 107 foreign workers were freed.

The Algerians were released early in the standoff — former hostages said the attackers immediately separated out the foreigners, forcing some to wear explosive belts.

In this image made from video, individuals believed to be hostages kneel in the sand with their hands in the air at an unknown location in Algeria. (Ennahar TV/Associated Press)

A former driver at the natural gas complex, originally from Niger, was among the band of al-Qaeda-linked militants, Sellal said.

Sellal said the heavily armed militants came from neighbouring Mali carrying a great deal of explosives and mined the facility. They had prepared the attack for two months.

The operation was led by an Algerian, Amine Benchenab, who was known to security services, he added.

Authorities have said the attack was under the command from afar of the one-eyed Algerian bandit Moktar Belmoktar, founder of the Masked Brigade, based in Mali.

• Mokhtar Belmokhtar, al-Qaeda's man in the Sahara?

Armed with heavy machine-guns, rocket launchers, missiles and grenades, the militants singled out foreign workers — from countries including Japan, Britain, the Philippines and Romania — at the plant, killing some of them on the spot and attaching explosive belts to others.

Algerian forces stormed the gas plant on Saturday, bringing the four-day hostage situation to a violent end. Algerian authorities began searching the refinery for explosive traps left behind by the attackers and found dozens more bodies.

At least 25 more bodies were found Sunday, but many were so badly disfigured that it was unclear whether they were hostages or militants, a security official said.

Some hostages still missing

Confirmed dead so far include:

• Six from the Philippines.
• Three from Britain.
• Two from Romania.
• One from France.
• Three from the U.S.
• Seven from Japan.

Algeria says five foreign hostages remain missing, but other governments say that figure is too low.

Japan's prime minister said Monday that seven Japanese citizens were confirmed dead at the gas plant. Prime Minister Shinzo Abe said that three other Japanese are still missing.

Three Americans were killed during the hostage-taking but seven made it out safely, an Obama administration official said Monday. The FBI has recovered the bodies of the Americans and notified their families, the official said, speaking on condition of anonymity because he wasn't authorized to speak publicly about the matter.

Rescue workers at the hospital in Ain Amenas, Algeria, carry the coffin of one of the hostages killed during the siege at the nearby gas plant. (Ramzi Boudina/Reuters)

The deceased Americans were identified as Victor Lynn Lovelady and Gordon Lee Rowan, the official said. One American death was confirmed Friday, that of Texas resident Frederick Buttaccio.

Many other hostages remain unaccounted for, including five Norwegian employees of Statoil, the energy company said Sunday. The U.K. government said three other Britons and a Colombian who lived in the U.K. are still missing.

Four Filipino workers are unaccounted for, said a government spokesman in Manila, and two Malaysians are missing, its government said.

With files from CBC News, The Canadian Press