Canada also expelled "a senior Indian diplomat" for India's alleged involvement in the killing.

Nijjar, who was spearheading the Khalistani referendum in Canada, was gunned down by two persons on June 18 in the parking lot of Surrey's Guru Nanak Sikh Gurdwara.

Trudeau told the House of Commons that the "agents of the Indian government" carried out Nijjar's killing.

The Canadian Prime Minister, who was snubbed in India during his recent visit, said: "Canadian security agencies have been actively pursuing credible allegations of a potential link between agents of the Government of India and the killing of a Canadian citizen, Hardeep Singh Nijjar."

Trudeau said: "Any involvement of a foreign government in the killing of a Canadian citizen on Canadian soil is an unacceptable violation of our sovereignty. It is contrary to the fundamental rules by which free, open, and democratic societies conduct themselves.

"As you would expect, we have been working closely and coordinating with our allies on this very serious matter."

Trudeau said that he brought the issue to the notice of the Indian Prime Minister during his visit. "Canada declared its deep concerns to the top intelligence and security officials of the Indian government last week at the G20. I brought them personally and directly to Prime Minister Modi."

He said because of Nijjar's killing, Canadians are now "angry" and "perhaps frightened right now". "Canada is a rule of law country. The protection of our citizens and defence of our sovereignty are fundamental."

Expelling the senior Indian diplomat, Foreign Affairs Minister Melanie Joly said: "My expectations are clear. I expect India to fully collaborate with us and get to the bottom of this."

She said Canada has informed US President Joe Biden and UK Prime Minister Rishi Sunak about its decision.

Canada's Public Safety Minister Dominic LeBlanc, under whom the Royal Canadian Mounted Police is investigating the killing, said: "We'll hold the perpetrators accountable and bring them to justice."