India and Canada each expelled the other's ambassador and five other top diplomats, after New Delhi said its envoy had been named among "persons of interest" following the killing of a Sikh separatist leader.
New Delhi said it was withdrawing its six diplomats from Canada, but an Ottawa government source told AFP they had been expelled, not withdrawn.
The 2023 murder of Canadian citizen Hardeep Singh Nijjar crashed the country's diplomatic relations with India after Prime Minister Justin Trudeau said there were "credible allegations" linking Indian intelligence services to the crime.
The expulsion of the diplomats -- the most senior envoys on both sides -- is a major escalation in the row.
India "decided to expel" Ottawa's acting High Commissioner Stewart Wheeler, his deputy and four first secretaries, ordering they leave before midnight on Sunday.
Ottawa announced similar measures in return, with Canadian police saying they had "evidence pertaining to agents of the government of India's involvement in serious criminal activity" in Canada.
Nijjar -- who immigrated to Canada in 1997 and became a citizen in 2015 -- had advocated for a separate Sikh state, known as Khalistan, carved out of India.
He had been wanted by Indian authorities for alleged terrorism and conspiracy to commit murder.
Four Indian nationals have been arrested in connection with Nijjar's murder, which took place in the parking lot of a Sikh temple in Vancouver in June 2023.
New Delhi had earlier said it had "received a diplomatic communication from Canada suggesting that the Indian High Commissioner and other diplomats are persons of interest" in the ongoing investigation.
It said their envoy, Sanjay Kumar Verma, a former ambassador to Japan and Sudan, was a respected career diplomat and that the accusations were "ludicrous".
New Delhi's foreign ministry said it had told Verma to return home.
"We have no faith in the current Canadian Government's commitment to ensure their security," it said in a statement.
'Murder'
India on Monday called allegations it was connected to the killing "preposterous" and a "strategy of smearing India for political gains".
Last year, the Indian government briefly curbed visas for Canadians and forced Ottawa to withdraw diplomats, and on Monday threatened further action.
"India reserves the right to take further steps in response to the Trudeau Government's support for extremism, violence and separatism against India," the foreign ministry said.
The foreign ministry also summoned Canadian envoy Wheeler, who said that Ottawa had given India the evidence it had demanded.
"Canada has provided credible, irrefutable evidence of ties between agents of the Government of India and the murder of a Canadian citizen on Canadian soil," Wheeler told reporters after leaving the ministry.
"Now, it is time for India to live up to what it said it would do and look into all those allegations. It is in the interest of both our countries and the peoples of our countries to get to the bottom of this. Canada stands ready to cooperate with India."
India then announced his expulsion.
Canada is home to around 770,000 Sikhs, who make up about two percent of the country's population, with a vocal minority calling for an independent state of Khalistan.
In November 2023, the US Justice Department also charged an Indian citizen living in the Czech Republic with allegedly plotting a similar assassination attempt on US soil.
Prosecutors said in unsealed court documents that an Indian government official was also involved in the planning of that attempt.