"A Canadian was among the militants," Prime Minister Abdelmalek Sellal told reporters at an Algiers news conference. "He was coordinating the attack."
Another Canadian was among the extremists who attacked the plant Wednesday and held hostages until Algerian forces ended the siege with a counter-attack Saturday, Sellal said.
Sellal identified the alleged coordinator by a single name, Shadad, or perhaps Sheddad, and did not say if he was killed or was among the three attackers who survived.
He said Algeria believed the man was Canadian, "judging by his English accent."
Sellal did not identify the second possible Canadian.
Canada's government said it was investigating the assertions.
"We are in close contact with Algerian authorities, but nothing confirmed yet," Canadian Foreign Affairs Ministry spokeswoman Chrystiane Roy told The Globe and Mail in an email message.
Sellal told reporters the attackers had come from Canada, Egypt, Mali, Mauritania, Niger and Tunisia. He did not say how he knew this.
A video sent to a Mauritania media outlet by the Islamist al-Mulatahemeen, or the Masked Brigade, organization -- also known as al-Muaqioon Biddam, or Those Who Sign With Blood Brigade -- claimed responsibility for the attack.
The group's leader, Mokhtar Belmokhtar, said in the video cited by Mauritania's Sahara Media the attackers had come "from Muslim countries and some even from Western countries."
Belmokhtar's group is a splinter faction of al-Qaida in the Islamic Maghreb. In the video, Belmokhtar claimed direct allegiance with al-Qaida.
"We in al-Qaida announce this blessed operation," he was quoted by Sahara Media as saying. The West African news website, monitored by United Press International, did not immediately post the video online.
Norwegian newspaper Aftenposten quoted an Algerian military source as saying one of the kidnappers was tall and blond with blue or green eyes. The source also said he spoke English and read the Koran, the sacred book of Muslims.
The U.S. State Department said Monday two additional Americans died during the siege at the vast Ain Amenas field in the Sahara near Libya, bringing the total to three.
Spokeswoman Victoria Nuland identified them as Gordon Lee Rowan and Victor Lynn Lovelady, without specifying their hometowns. The department Friday identified the first person reported killed as Frederick Buttacio of Katy, Texas.
Rep. Greg Walden, R-Ore., said in a statement Monday Rowan, 59, lived with his family in Sumpter, Ore.
Lovelady, 58, of Nederland, Texas, was married and had two children.
"We extend our deepest condolences to their families and friends," Nuland said.
"The blame for this tragedy rests with the terrorists who carried it out, and the United States condemns their actions in the strongest possible terms," she said. "We will continue to work closely with the government of Algeria to gain a fuller understanding of the terrorist attack of last week and how we can work together moving forward to combat such threats in the future."
Nuland said seven Americans survived the crisis, but she did not identify them.
The siege began Wednesday when the al-Qaida-linked militants ambushed a bus carrying gas-field workers, were repelled, and then commandeered the gas compound, Sellal said.
The attackers appeared to be trying to escape with hostages Wednesday when Algerian military helicopters with missiles bombarded vehicles to prevent them from speeding away, he said.
The Algerian forces killed at least 29 of the 32 kidnappers, Sellal said.
The state-run Algeria Press Service said nearly 700 Algerians and 107 foreigners were freed or escaped from the gas field, operated by British multinational oil and gas company BP PLC in partnership with Norway's Statoil ASA and Algerian government-owned energy company Sonatrach.