Prime Minister Justin Trudeau of Canada said on Monday that “agents of the government of India” had carried out the assassination of a Sikh community leader in British Columbia in June, an explosive allegation that is likely to further sour relations between the two nations.
Speaking in the House of Commons, Mr. Trudeau said that he had raised India’s involvement in the shooting of the Sikh leader, Hardeep Singh Nijjar, directly with Prime Minister Narendra Modi at the Group of 20 summit meeting earlier this month “in no uncertain terms.”
He said the allegation was based on intelligence gathered by the Canadian government.
“Any involvement of a foreign government in the killing of a Canadian citizen on Canadian soil is an unacceptable violation of our sovereignty,” Mr. Trudeau told lawmakers.
He said Canada would pressure India to cooperate with the investigation into the killing of Mr. Nijjar, who advocated Sikh separatism.
Mélanie Joly, the foreign minister, later announced that Canada had expelled an Indian diplomat whom she described as the head of India’s intelligence agency in Canada.
India’s foreign ministry rejected the Canadian allegations on Tuesday morning as “absurd” and politically motivated, saying that Canada had long provided shelter to “Khalistani terrorists and extremists” who threaten India’s security.
Khalistan is what Sikh separatists call the independent state they seek to create.
The ministry said that Mr. Modi had “completely rejected” the allegations when Mr. Trudeau presented them to him.
“We urge the government of Canada to take prompt and effective legal action against all anti-India elements operating from their soil,” the ministry said in a statement.
It later said that it had moved to expel a senior Canadian diplomat based in India.
The allegation that India’s government was involved in a political killing in Canada is likely to further corrode relations between the two countries.
Earlier this month, Canada suspended negotiations on a trade deal with India that were scheduled to have been concluded this year — because of the assassination allegations, it now appears.
During the G20, Mr. Modi excluded Mr. Trudeau from the list of leaders with whom he held formal bilateral meetings.
Mr. Trudeau said many Canadians of Indian origin — they make up about 4 percent of the population — had been angered by the killing and in some cases feared for their personal safety.
There are about 1.4 million Canadians of Indian heritage, many of whom are Sikhs; they include Jagmeet Singh, the leader of the opposition New Democratic Party, which is keeping Mr. Trudeau’s minority government in power. Singh is a common surname and middle name in Punjab.
Mr. Nijjar, 45, was shot near a Sikh temple in Surrey, British Columbia. At a news conference in June, investigators from the Royal Canadian Mounted Police said he had been ambushed by masked men, but would not say whether the attack appeared politically motivated.
Mr. Nijjar was known for his advocacy of the creation of an independent Sikh nation, Khalistan, that would include parts of India’s Punjab state, and India had declared him a wanted terrorist.
Citing the police investigation, neither Ms. Joly nor Dominic LeBlanc, the minister of public safety, offered any details about Indian involvement in the killing.
But Mr. LeBlanc said that Jody Thomas, Mr. Trudeau’s national security adviser, as well as the head of Canada’s intelligence service, had traveled over the past few weeks “to confront the Indian intelligence agencies with these allegations.”
It was unclear from the two minister’s remarks how forthcoming the Indian government has been or what cooperation, if any, it has offered.
Ms. Joly said she planned to discuss India’s actions during meetings with Canada’s allies after she travels to New York this week for the United Nations General Assembly.
The announcement came on the same day that a judge opened a public inquiry into interference by foreign governments.
It was prompted by allegations that China is meddling in Canadian politics, but Mr. LeBlanc said that reviewing India’s actions are within the inquiry’s mandate. “Obviously these allegations are at a much more serious level,” he said.
Mr. Nijjar was vocal about the threats to his life, which were shared with Canada’s spy agency, the World Sikh Organization of Canada, a nonprofit, said in a statement.
“If these allegations are true, they represent an outrageous affront to Canada’s sovereignty,” said Pierre Poilievre, leader of the Conservative Party.
“Our citizens must be safe from extrajudicial killings of all kinds, most of all from foreign governments.”
Mr. Singh, the New Democratic Party leader, broke with protocol to address the House of Commons in Punjabi as well English and said he had spoken with Mr. Nijjar’s son.
“I could hear the pain of that loss in his voice,” Mr. Singh said. “I can only imagine how much more painful it is going to be.”