Information shared by members of an intelligence-sharing alliance was part of what Canadian Prime Minister Justin Trudeau used to make public allegations of the Indian government's possible involvement in the assassination of a Sikh Canadian, the U.S. ambassador to Canada said.

"There was shared intelligence among 'Five Eyes' partners that helped lead Canada to (make) the statements that the prime minister made," U.S. Ambassador David Cohen told Canadian CTV News network.

CTV News released some of Cohen's comments late Friday, and the network said that it would air the full interview with the U.S. envoy on Sunday. No further details were released about the shared intelligence.

On Thursday, a Canadian official told The Associated Press that the allegation of India's involvement in the killing is based on surveillance of Indian diplomats in Canada, including intelligence provided by a major ally - without saying which one.

The "Five Eyes" intelligence-sharing alliance is made up of Australia, Canada, New Zealand, the United Kingdom and the United States.

The relationship between Canada and India reached its lowest point in recent history when Trudeau said there were "credible allegations" of Indian involvement in the assassination of Hardeep Singh Nijjar, a 45-year-old Sikh separatist, in June in a Vancouver suburb. Both countries have expelled some top diplomats.

India, which has called the allegations "absurd," also has stopped issuing visas to Canadian citizens and told Canada to reduce its diplomatic staff.

Canada has yet to provide public evidence to back Trudeau's allegations.

Nijjar, a plumber who was born in India and became a Canadian citizen in 2007, had been wanted by India for years before he was gunned down in June outside the temple he led in Surrey, a suburb of Vancouver.