India has told Canada to withdraw dozens of diplomats from the country, in an escalation of the crisis that erupted when Prime Minister Justin Trudeau said New Delhi may have been linked to the murder of a Canadian Sikh.

Ottawa has been told by New Delhi that it must repatriate roughly 40 diplomats by October 10, according to people familiar with the demand. One person said India had threatened to revoke the diplomatic immunity of diplomats who remain after that date.

The Canadian foreign ministry and the Indian government declined to comment. New Delhi has previously said it wanted “parity” in the number and grade of diplomats each nation posts to the other.

Canada has several dozen more diplomats at its high commission in New Delhi than India has in Ottawa, because of the big consular section needed for relatives of the roughly 1.3mn Canadians who claim Indian heritage.

One person said Canada had 62 diplomats in India and that New Delhi had told them to reduce that by 41 people.

New Delhi already announced a visa ban for Canadians the day after Trudeau made his bombshell claim on September 18.

The latest move threatens to significantly intensify the crisis that broke when Trudeau said Ottawa was investigating “credible allegations” that Indian agents may be behind the assassination of Hardeep Singh Nijjar, a Sikh separatist and Canadian citizen, who was killed in a Vancouver suburb in June.

It will also complicate matters for Trudeau, who faces pressure at home to act while also trying to secure support from western allies who are eager to foster relations with New Delhi to serve as a bulwark to China.

“Declaring more Canadian diplomats personae non gratae wouldn’t help the situation and would make reducing the emotions associated with this disagreement more difficult,” said Peter Boehm, chair of the Canadian Senate committee on foreign affairs and international trade.

Trudeau’s claim followed frustration in Ottawa that weeks of secret diplomacy with India had failed to secure its co-operation with the police inquiry into Nijjar’s murder.

The diplomacy included two trips by Canadian national security adviser Jody Thomas to India to discuss the issue ahead of the G20 in New Delhi in September. India did not admit involvement in the murder, but did not deny the claim, according to people familiar with the meetings. The Indian government said it had rejected the allegations.

The murder was also the focus of Trudeau’s meeting with India’s prime minister Narendra Modi at the G20, when the Indian side flatly refused a request for co-operation. In earlier meetings, India had even urged Canada to halt the inquiry, according to people familiar with the case.

India’s foreign minister S Jaishankar said in Washington last week that the alleged assassination was “not consistent with our policy” and accused Canada of indulging Sikh separatists agitating for an independent state in India.

Canadian media has reported that Ottawa has intercepts of conversations involving Indian diplomats that point to official involvement in Nijjar’s shooting last June. India has denied seeing any such evidence.

Ottawa is limited in what it can share with the Indian government, partly to protect the sources and methods used to collect the intelligence, but also to avoid compromising the murder investigation, according to people familiar with the matter.

The constraints meant Thomas and other officials who visited India, including Canadian Security Intelligence Service head David Vigneault, had only been able to present the evidence orally to their Indian counterparts.

The stand-off with India is a problem for Trudeau, whose popularity is waning during a cost of living crisis while his Liberal party gears up for elections due before October 2025. Critics have charged Trudeau with pandering to Canada’s sizeable Sikh population and acting rashly.

It was “not a great time” for the crisis, said one person familiar with his thinking. But Trudeau felt compelled to make a statement in parliament ahead of a planned article in The Globe and Mail newspaper and because of the seriousness of the allegations, said people familiar with the matter.

“A Canadian was killed on Canadian soil. This is about sovereignty, so it had to be the PM [making the statement],” said one of the people.

Roland Paris, a foreign policy expert at the University of Ottawa, said the nature of the allegations had left Trudeau with little choice.

“There is a sense in Canada that bad things happen elsewhere, but this murder has really punched into the public consciousness,” said Paris. “It is not something Canada or Canadians are going to brush aside or forget.”

Richard Fadden, a former head of the CSIS who served as Trudeau’s national security adviser, said he had been surprised by the prime minister’s move. “I thought he must be absolutely certain about the evidence.”

While some Canadian critics were initially disappointed by the reaction of its international allies to its “credible allegations” against India, the tone has shifted.

The Financial Times recently reported that President Joe Biden raised Nijjar’s murder with Modi at the G20. Secretary of state Antony Blinken last week urged India to co-operate with the Canadian police investigation.

David Cohen, US ambassador to Ottawa, has also said Canada received intelligence on the murder from the “Five Eyes” intelligence-sharing network, which also includes the US, UK, Australia and New Zealand — a statement that will bolster Trudeau’s case.

“I do not expect the prime minister to back down,” said Boehm, who also warned that India saw Canada as “an easy mark”.

“India knows our capacity to retaliate is limited, that we have a minority government, and is aware of the consequent politics at play,” said Boehm. “And, of course, India has an election on the horizon.”

Vina Nadjibulla, a professor at the University of British Columbia, said the spat had put Canada and its allies in a “difficult spot” and that it was hard to see how Ottawa and New Delhi could calm relations for some time.

“It is difficult to see anything changing while the leadership in both countries stays the same,” she said.

Additional reporting by John Reed in New Delhi