Canada’s prime minister has said Canadian security agencies are investigating “credible allegations of a potential link” between Indian government agents and the killing of a prominent Sikh-Canadian activist earlier this year.

Speaking in Parliament on Monday afternoon, Justin Trudeau said he personally conveyed “deep concerns” to his Indian counterpart, Narendra Modi, at the Group of 20 summit in New Delhi earlier this month.

Hardeep Singh Nijjar was fatally shot on June 18 outside a Sikh temple in Surrey, a city in Canada’s westernmost province of British Columbia, spurring widespread questions and condemnation.

“Any involvement of a foreign government in the killing of a Canadian citizen on Canadian soil is an unacceptable violation of our sovereignty,” Trudeau said on Monday.

“In the strongest possible terms, I continue to urge the government of India to cooperate with Canada to get to the bottom of this matter.”

The High Commission of India in the Canadian capital Ottawa did not immediately return Al Jazeera’s request for comment on the allegations.

Canadian Foreign Minister Melanie Joly said later on Monday that the government had expelled an Indian diplomat – the head of India’s external intelligence agency, known as RAW, in Canada – over the allegations.

She did not provide additional details, such as the official’s name or when the expulsion took place.

“We see this possible breach of sovereignty as completely unacceptable, and so that is also why we’re coming [out] with this information today,” Joly told reporters during a brief news conference.

The Globe and Mail newspaper first reported that Canadian national security authorities have “what they consider credible intelligence that India was behind” the killing of Nijjar.

Sources that spoke to the Canadian news outlet did not say how they made that determination.

“The Canadian government has privately ruled out severing diplomatic relations with New Delhi but is considering measures to respond to what it considers a serious violation of Canadian sovereignty,” the newspaper reported, citing unnamed sources.

Strained relations

Monday’s accusations come amid already strained relations between Ottawa and New Delhi, which have been tested over a range of issues including a stalled trade deal and Sikh activism in Canada more broadly.

Modi, the Indian prime minister, expressed “strong concerns” about Sikh protests in Canada during his talks with Trudeau on the sidelines of the G20, the Indian government said in a statement after the discussions.

“They are promoting secessionism and inciting violence against Indian diplomats, damaging diplomatic premises, and threatening the Indian community in Canada and their places of worship,” the statement said.

According to the Globe and Mail and other media reports, Nijjar was designated as a “terrorist” by the Indian authorities.

“India’s counter-terrorism National Investigation Agency (NIA) has alleged he conspired to kill a Hindu priest in Punjab and in 2022 it announced a reward equivalent to $16,200 for information leading to his arrest,” the Canadian newspaper said on Monday.

The activist was also involved with a group called “Sikhs for Justice”, CBC News has reported. The organisation pushes for an independent Sikh state in India, a call the Indian authorities have rejected outright.

Canadian lawmakers from across the political spectrum were quick to denounce India on Monday for its potential role in the activist’s killing.

Pierre Poilievre, the leader of the opposition Conservative Party, said in the House of Commons that if if the allegations are true, they would represent an “outrageous affront” to Canadian sovereignty.

“Canadians deserve to be protected on Canadian soil,” Poilievre said. “We call on the Indian government to act with utmost transparency as authorities investigate this murder because the truth must come out.”

Canadian authorities continue to investigate Nijjar’s killing, with the Royal Canadian Mounted Police (RCMP) saying last month that they had identified a vehicle believed to have been involved in the incident. Authorities say they are looking for three suspects.

Jagmeet Singh, the leader of the progressive New Democratic Party (NDP), who is of Sikh descent, said it was important for Canada to use “every tool” available to investigate the killing.

“We need to know the truth. We need to know all potential links, and anyone and everyone responsible should be brought to justice using the full power of a democratic nation,” Singh said.