Canada is investigating an allegation by the Algerian Prime Minister that one of its citizens co-ordinated the terror raid at the Saharan gas plant in which dozens of hostages were killed.

Westerners, including a man with blond hair and blue eyes, are believed to have been among the Islamist militants who launched last week’s attack on the Tigantourine complex near Algeria’s border with Libya.

A French jihadist, previously unknown to authorities, and two Canadians are suspected to have been involved in the hostage-taking, and reports also claim that a man with a Western accent was among the extremists who lured terrified gas workers from their rooms during the hostage crisis.

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Prime Minister Abdelmalek Sellal told reporters that a man, judged “by his English accent” to have been Canadian, was among the 32 Islamists whose raid on the Algerian refinery prompted a global crisis. One of the Canadians, identified only as “Shaddad”, is alleged to have played a leading role in the attack which left 58 hostages – including 37 Westerners - dead after a four-day battle with Algerian forces. Five further Western workers are still unaccounted for. “A Canadian was among the militants,” Mr Sellal said. “He was co-ordinating the attack.”

The militant group also included men from Tunisia, Egypt, Mauritania and Niger, Mr Sellal said. At least 29 Islamists from eight nationalities were killed in the operation to end the siege, with the remaining three captured alive. The make up of the attacking group – an al-Qa’ida splinter brigade who call themselves “Those Who Signed in Blood” - will be carefully examined as security experts try to assess the scale of the terror threat across North and West Africa.

Concern at the international composition of the Algerian kidnap brigade will be compounded by reports from residents in Diabaly, Mali, that Islamists who overran the town last week contained English-speakers and militants of European appearance. Speaking to The Independent yesterday after French and Malian forces had retaken the town, student Amadu Dumbia said: “I definitely heard them and there’s no chance that I made a mistake with another language. They spoke like they were from England, but had darker skins.”

Mokhtar Belmokhtar, the leader of the group who is suspected of masterminding the gas plant attack from outside Algeria, yesterday warned that there would be more attacks on those participating in the military campaign in neighbouring Mali. In a statement to a radio station in Mauritania, which received regular communications from the militants during the In Amenas plant siege, the Algerian-born militant said: “We warn all the states who took part in the Crusader campaign against the Azwad region [northern Mali] that if they do not retreat from their decision there will be more operations.”

He also insisted that the brigade which undertook the attack was not local, saying “only five Algerians” took part in the attack and “none of them were locals from the city”.

Prime Minister David Cameron today told the Commons that the West faced a “generational struggle” in combating the “poisonous ideology” of Islamic extremists in the Sahel. Mr Cameron said that Britain would join the manhunt for Belmokhtar and promised extra support for the French campaign in Mali. Echoing the language used by Tony Blair in the aftermath of the September 11 attacks on the World Trade Centre, he said: “This is the work our generation faces and we must demonstrate the same resolve and sense of purpose as previous generations have with the challenges that they faced in this House and in this country.”

A spokeswoman for Canada’s Foreign Affairs Ministry yesterday said that they were still seeking clarity on a possible Canadian connection to the raid. “We are in close contact with Algerian authorities, but nothing [has been] confirmed yet,” Chrystiane Roy told Canada’s Globe and Mail newspaper.

The Algerian authorities have declined to confirm whether the alleged Canadian co-ordinator was among the 29 militants who died.

One of the hostage takers was a North American who took part in the killing of numerous Japanese workers, the AFP agency reported. An Algerian employee of a Japanese engineering firm working at the site, identified as Riad said the Islamist attackers shot three Japanese who were in a bus, then went straight to the rooms occupied by the Japanese.

“One terrorist shouted ‘Open the door’ with a North American accent, then fired,” he told AFP. “Two other Japanese died and we found four other Japanese bodies inside the base.”

One of the kidnappers was tall, blond with blue or green eyes and spoke English, an Algerian military source told the Norwegian daily Aftenposten. Norway’s Statoil energy company was one of the two foreign firms operating at the gas complex.