Canada expelled a top Indian diplomat as it investigates what Prime Minister Justin Trudeau called credible allegations its government may have had links to the assassination in Canada of a Sikh activist, an accusation that India rejected as “absurd.”

Trudeau said in Parliament on Monday that Canadian intelligence agencies have been looking into the allegations after Sikh leader Hardeep Singh Nijjar, a strong supporter of an independent Sikh homeland known as Khalistan, was gunned down on June 18 outside a Sikh cultural center in Surrey, British Columbia.

Trudeau told Parliament that he brought up the slaying with Indian Prime Minister Narendra Modi at the Group of 20 summit last week in New Delhi. He said he told Modi that any Indian government involvement would be unacceptable and that he asked for cooperation in the investigation.

Canadian Foreign Minister Mélanie Joly said the head of Indian intelligence in Canada has been expelled as a consequence.

“If proven true this would be a great violation of our sovereignty and of the most basic rule of how countries deal with each other,” Joly said. “As a consequence we have expelled a top Indian diplomat.”

India’s foreign ministry dismissed the allegation of government involvement as “absurd and motivated.” The ministry’s statement Tuesday added that Trudeau made similar allegations to Modi at the G20 summit.

“Such unsubstantiated allegations seek to shift the focus from Khalistani terrorists and extremists, who have been provided shelter in Canada and continue to threaten India’s sovereignty and territorial integrity,” the statement noted, referring to a separatist movement India regards as a security threat.

The expulsion comes as relations between Canada and India are tense. Trade talks have been derailed and Canada just canceled a trade mission to India that was planned for the fall.

During a meeting with Trudeau at the G20 summit, Modi expressed “strong concerns” over Canada’s handling of the Punjabi independence movement among overseas Sikhs, according to India’s Ministry of External Affairs.

The statement described the Sikh movement as “promoting secessionism and inciting violence” against Indian diplomats. It called on Canada to work with India on what New Delhi said is a threat to the Canadian Indian diaspora.

Canada has a Sikh population of more than 770,000, or about 2% of its total population.

“Over the past number of weeks 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.

Trudeau said Canada has declared its deep concerns to the Indian government. “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 his government has been working closely and coordinating with Canada’s allies on the case.

“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,” he said.

Public Safety Minister Dominic LeBlanc said Canada’s national security adviser and the head of Canada’s spy service have travelled to India to meet their counterparts and to confront the Indian intelligence agencies with the allegations.

He called it an active homicide investigation led by the Royal Canadian Mounted Police.

Joly said Trudeau also raised the matter with U.S. President Joe Biden and U.K. Prime Minister Rishi Sunak.

“We are deeply concerned about the allegations referenced by Prime Minister Trudeau,” White House National Security Council spokesperson Adrienne Watson. “We remain in regular contact with our Canadian partners. It is critical that Canada’s investigation proceed and the perpetrators be brought to justice.”

Opposition New Democrat leader Jagmeet Singh, who is himself Sikh, called it outrageous and shocking. Singh said he grew up hearing stories that challenging India’s record on human rights might prevent you from getting a visa to travel there.

“But to hear the prime minister of Canada corroborate a potential link between a murder of a Canadian citizen on Canadian soil by a foreign government is something I could never have imagined,” Singh said.

The Khalistan movement is banned in India, where officials see it and affiliated groups as a national security threat. But the movement still has some support in northern India, as well as beyond, in countries like Canada and the United Kingdom which are home to a sizable Sikh diaspora.

Nijjar was organizing an unofficial referendum in India for an independent Sikh state at the time of this death. Indian authorities announced a cash reward last year for information leading to Nijjar’s arrest, accusing him of involvement in an alleged attack on a Hindu priest in India.

British Columbia Premier David Eby said he’s received a briefing from Canada’s spy agency about the “assassination” of Nijjar and he’s “deeply disturbed” by what he was told.