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 told The Associated Press on Thursday.

The official said 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 includes the U.S., Britain, Australia and New Zealand, in addition to Canada.

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

Also read: How India’s relations with Canada hit rock bottom

The Canadian Broadcasting Corporation first reported the intelligence.

The revelation came as India stopped issuing visas to Canadian citizens and told Canada to reduce its diplomatic staff as the rift widened over allegations by Prime Minister Justin Trudeau of suspected Indian involvement in the killing of Hardeep Singh Nijjar, a 45-year-old Sikh separatist.

Ties between the two countries have plunged to their lowest point in years after Trudeau told Parliament Monday there were "credible allegations" of Indian involvement in the assassination on Canadian soil.

Also read: India asks citizens to be careful if traveling to Canada as rift widens over Sikh leader’s death

Nijjar, a plumber who was born in India and became a Canadian citizen in 2007, had been wanted by India for years before he was gunned down in June outside the temple he led in Surrey, a suburb of Vancouver.

Speaking Thursday on the sidelines of the U.N. General Assembly, Trudeau acknowledged the complicated diplomatic situation.

"The decision to share these allegations on the floor of the House of Commons was not done lightly," he said. "There is no question that India is a country of growing importance and a country that we need to continue to work with."

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

Also read: India suspends visa services for Canadians amid diplomatic row

Canada has yet to provide public evidence to back Trudeau's allegations, and Canada's U.N. ambassador, Bob Rae, indicated that might not come soon.

"This is very early days," Rae told reporters Thursday, saying 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.

Meanwhile, the company that processes Indian visas in Canada announced services had been suspended. Canadians are among the top travelers to India, with 277,000 Canadian tourists visiting the country in 2022, 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.

Also read: Who was Hardeep Singh Nijjar, the Sikh activist whose killing has divided Canada and India?

"Security threats being faced by our High Commission and consulates in Canada have disrupted their normal functioning," Bagchi told reporters. He gave no details on the alleged threats.

The announcement quickly rippled across Canada, especially among people with ties to India.

Maitreyi Bhatt, a 27-year-old Indian citizen whose partner is Canadian and needs a visa, was distraught because her wedding is scheduled for late October in India, when he was to meet her family for the first time.

"I've been crying all day," she said. "It's so difficult. I was just so excited for him to meet my family."

She said the venue is booked and the couple has non-refundable flights. She said her partner went to the Indian Consulate in Toronto but was escorted out by security.

Also read: What to know about the Sikh movement at the center of the tensions between India and Canada

"People like me are just caught up in this and it's just not fair," she said.

Sukhwinder Dhillon, a 56-year-old grocery store owner in Montreal, said he had a trip planned to India to see family and sort out his deceased father's estate. Dhillon, who came to Canada in 1998, makes the trip every two or three years and has lost two family members since he was last home.

"My father passed, and my brother passed," Dhillon said. "I want to go now. ... Now I don't know when we'll go."

Bagchi, the Indian foreign ministry spokesman, also called on Canada to cut its diplomatic corps in India, saying they outnumbered Indian diplomats in Canada.

The Canadian High Commission in New Delhi said Thursday that its consulates in India were open and continue to serve clients. It said some of its diplomats had received threats on social media, adding that Canada expects India to provide security for its diplomats and consular officers working there.

Also read: Canada expels Indian diplomat as it investigates Sikh activist's killing

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

India's security and intelligence branches have long been active in South Asia and are suspected in a number of killings in Pakistan. But arranging the killing of a Canadian citizen in Canada, home to nearly 2 million people of Indian descent, would be unprecedented.

India has criticized Canada for years over giving free rein to Sikh separatists, including Nijjar. New Delhi had accused him of 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 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% of the population, to do more to stop them.

At the time of his killing, Nijjar was working to organize 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.

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.

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 canceled a trade mission to India planned for the fall. A trade deal between the two is now on pause.