The United States has joined Canada in calling for India to reveal what it knows about the slaying of Sikh leader Hardeep Singh Nijjar, and Reuters news agency said Canada worked closely with US on India's possible link to Nijjar's killing.
"We are deeply concerned about the allegations referenced by Prime Minister Trudeau," National Security Council spokesperson Adrienne Watson said in a statement on Tuesday.
"We remain in regular contact with our Canadian partners. It is critical that Canada's investigation proceed and the perpetrators be brought to justice."
Nijjar, a Sikh leader in the western Canadian province of British Columbia, was shot dead on June 18 in front of a Sikh temple in Surrey.
Meanwhile Reuters citing a senior Canadian government source said Canada worked "very closely" with the United States on intelligence that Indian agents had been potentially involved in the case.
"We've been working with the US very closely, including on the public disclosure yesterday," the source told Reuters.
The evidence in Canada's possession would be shared "in due course", said the official who spoke on condition of anonymity due to the sensitivity of the information.
Prime Minister Trudeau on Tuesday told reporters that the case had far-reaching consequences in international law and urged the Indian government to take the matter seriously and help Canada fully investigate the matter.
India quickly dismissed Trudeau's assertion as "absurd" and said it was expelling a Canadian diplomat, a tit-for-tat move after Canada expelled India's top intelligence figure on Monday.
The dispute deals a fresh blow to diplomatic ties that have been fraying for years, with New Delhi unhappy over Sikh separatist activity in Canada.
The spat has already thrown cold water on trade talks, which have been paused, and Canada last week called off a major trade mission scheduled for October.
A second Canadian source familiar with the situation said that both the pause in the trade talks and the delay of the trade mission were due to the concerns surrounding the murder of the Canadian.
New Delhi, which has urged Ottawa to act against "anti-Indian" elements, has long been unhappy over Sikh separatist activity in Canada.
Nijjar supported creating a Sikh homeland in the form of an independent, so-called state of Khalistan in India's northern state of Punjab, the birthplace of the Sikh religion, which borders Pakistan.
India designated Nijjar as a "terrorist" in 2020.
Nijjar has become the fourth Sikh activist mysteriously killed in little over a year.