Toronto: Though Canadian Prime Minister Justin Trudeau on Thursday clarified that the country is not looking to "provoke or cause problems" with India amid the escalating diplomatic tension, he seems to be determined to prove the veracity of his claims.

The allegation of India's involvement in the killing of a Sikh Canadian is based on surveillance of Indian diplomats in Canada, including intelligence provided by a major ally, a Canadian official familiar with the matter has told The Associated Press.

The official said on Thursday that the communications involved Indian officials and Indian diplomats in Canada and that some of the intelligence was provided by a member of the "Five Eyes" intelligence-sharing alliance, which in addition to Canada includes the US, Britain, Australia and New Zealand.

The official, who spoke on condition of anonymity because they were not authorised to discuss the matter publicly, did not say which ally provided intelligence or give specific details of what was contained in the communications or how they were obtained.

The Canadian Broadcasting Corporation first reported details of the intelligence. The intelligence did not come solely from Canada. Some were provided by an unnamed ally in the Five Eyes intelligence alliance, the public broadcaster said.

The report said the diplomatic crisis unfolded progressively behind the scenes. Canadian officials went to India on several occasions seeking cooperation in the investigation of Nijjar's death, the report claimed.

US supports Canada

The US on Thursday said it supports Canada's efforts to investigate allegations of India's involvement in the killing of a Sikh separatist leader in Surrey, observing that no country can get any "special exemption" for such kind of activities.

As soon as we heard from the Canadian Prime Minister publicly about the allegations, we went out publicly ourselves and expressed our deep concern about them, our support for a law enforcement process to get to the bottom of exactly what happened, and to ensure that the perpetrators are held accountable, National Security Advisor Jake Sullivan told reporters at a White House news conference.

The NSA said the US has been and will be in contact with India on this issue.

Reduction in diplomatic staff

Earlier Thursday, India told Canada to reduce its diplomatic staff and stopped issuing visas to Canadian citizens as a rift widened between the once-close allies over Ottawa's allegation that New Delhi may have been involved in the killing of the Canadian citizen.

Ties between the two countries key strategic partners in security and trade have plunged to their lowest point in years since Canadian Prime Minister Justin Trudeau said there were "credible allegations" of Indian involvement in the assassination of the Sikh separatist activist in June in a Vancouver suburb.

Hardeep Singh Nijjar, a 45-year-old Canadian citizen who had been wanted by India for years, was gunned down outside the temple he led in the city of Surrey. Nijjar, a plumber, was born in India but became a Canadian citizen in 2007.

The Canadian High Commission in New Delhi said Thursday that all its consulates in India are open and continue to serve clients. It said some of its diplomats had received threats on social media, prompting it to assess its "staff complement in India". It added that Canada expects India to provide security for its diplomats and consular officers working there.

On Wednesday, India warned its citizens to be careful when travelling to Canada because of "growing anti-India activities and politically condoned hate crimes".

Speaking on the sidelines of the UN General Assembly, Trudeau acknowledged the complicated diplomatic situation he faced.

"There is no question that India is a country of growing importance and a country that we need to continue to work with," he said. "We are not looking to provoke or cause problems but we are unequivocal around the importance of the rule of law and unequivocal about the importance of protecting Canadians."

The bombshell Monday allegation by Trudeau set off an international tit-for-tat, with each country expelling a diplomat. India called the allegations "absurd".

Canada has yet to provide any public evidence to back Trudeau's allegations, and Canada's UN ambassador, Bob Rae ,indicated Thursday that it might not come very soon. "This is very early days," Rae told reporters at the United Nations, insisting that while facts will emerge, they must "come out in the course of the pursuit of justice".

"That's what we call the rule of law in Canada," he said.

Visa services suspended

On Thursday, the company that processes Indian visas in Canada announced that visa services had been suspended until further notice. The BLS Indian Visa Application Centre gave no further details.

The suspension means Canadians who don't already have visas will not be able to travel to India until services resume. Canadians are among the top travellers to India. In 2021, 80,000 Canadian tourists visited the country, according to India's Bureau of Immigration.

Indian External Affairs Ministry spokesperson Arindam Bagchi blamed the visa suspension, which includes visas issued in third countries, on safety issues.

"Security threats being faced by our High Commission and consulates in Canada have disrupted their normal functioning. Accordingly, they are temporarily unable to process visa applications," Bagchi told reporters. "We will be reviewing the situation on a regular basis."

He gave no details on the alleged threats.

Bagchi also called for a reduction in Canadian diplomats in India, saying they outnumbered Indian diplomats in Canada.

"We have informed the Canadian government that there should be parity" in staffing, he said.

Bagchi accused Canada of providing a safe haven for terrorists. He said India has regularly provided Canada with specific evidence about criminal activities by people based on its soil, but the information has not been acted upon.

India has criticised Canada for years over giving free rein to Sikh separatists, including Nijjar. New Delhi had accused him of having links to terrorism, which he denied.

Nijjar was a local leader in what remains of a once-strong movement to create an independent Sikh homeland, known as Khalistan. A bloody decade-long Sikh insurgency shook north India in the 1970s and 1980s until it was crushed in a government crackdown in which thousands of people were killed, including prominent Sikh leaders.

While the active insurgency ended decades ago, the Indian government has warned that Sikh separatists are trying to stage a comeback and pressed countries like Canada, where Sikhs comprise over 2 per cent of the population, to do more to stop them.

At the time of his killing, Nijjar was working to organise an unofficial Sikh diaspora referendum on independence from India.

New Delhi's anxieties about Sikh separatist groups in Canada have long been a strain on the relationship, but the two have maintained strong defence and trade ties and share strategic interests over China's global ambitions.

In March, Indian Prime Minister Narendra Modi's government summoned the Canadian high commissioner in New Delhi, its top diplomat in the country, to complain about Sikh independence protests in Canada.

But signs of a broader diplomatic rift emerged at the summit of the Group of 20 leading world economies hosted by India earlier this month. Trudeau had frosty encounters with Modi, and a few days later Canada cancelled a trade mission to India planned for the fall. A trade deal between the two is now on pause.

(With inputs from AP via PTI.)