Canadian police have arrested members of an alleged hit squad investigators believe was tasked by the government of India with killing Khalistan separatist Hardeep Singh Nijjar in Surrey, according to a media report on Friday.

The ties between India and Canada came under severe strain following Canadian Prime Minister Justin Trudeau's allegations in September last year of the "potential" involvement of Indian agents in the killing of Nijjar.

New Delhi rejected Trudeau's charges as "absurd".

Quoting sources close to the investigation, the Canadian Broadcasting Corporation reported that the police are actively investigating possible links to three additional murders in Canada, including the shooting death of an 11-year-old boy in Edmonton.

Members of the hit squad are alleged to have played different roles as shooters, drivers and spotters on the day Nijjar was killed at the Guru Nanak Sikh Gurdwara in Surrey in British Columbia, according to the sources.

The men were arrested Friday during police operations in at least two provinces.

Sources said investigators identified the alleged hit squad members in Canada some months ago and have been keeping them under tight surveillance. Police are expected to announce the arrests and share some details of their investigation later Friday, the report said.

Nijjar, a 45-year-old Canadian citizen, was shot dead on June 18, shortly after evening prayers at his Guru Nanak Sikh Gurdwara in Surrey.

India had on Thursday rejected fresh comments by Prime Minister Trudeau on the killing of Nijjar and said the remarks once again illustrated the political space given in Canada to separatism, extremism, and violence.

Trudeau addressed a Khalsa Day event in Toronto on Sunday that was attended by some pro-Khalistan people.

On the sidelines of the event, he told the media that the killing of Nijjar in British Columbia in June last year created a "problem" and that he cannot ignore it, in an apparent reference to his earlier allegations of involvement of Indian agents in the assassination.

"PM Trudeau has made such remarks earlier as well. His remarks illustrate once again the political space that has been given in Canada to separatism, extremism, and violence," external affairs ministry spokesperson Randhir Jaiswal said in New Delhi at his weekly media briefing.

"This not only impacts India-Canada relations but also encourages a climate of violence and criminality in Canada to the detriment of its own citizens," he said when asked about Trudeau's remarks.

In his comments to the media, Trudeau, referring to activities by pro-Khalistani elements, said that "our job is not to crack down on political protest".

India on Monday summoned the Canadian deputy high commissioner and lodged a strong protest with him over the raising of pro-'Khalistan' slogans at the event in the presence of Trudeau and several other leaders. Nijjar was a Khalistani separatist and he was wanted in India on various terror charges.

"It is a problem in our relations with India because we cannot ignore that," Trudeau said on the killing of Nijjar.

Days after Trudeau's allegations, India asked Ottawa to downsize its diplomatic presence in the country to ensure parity. Subsequently, Canada withdrew 41 diplomats and their family members from India.

India has been asserting that its "core issue" with Canada remained that of the space given to separatists, terrorists and anti-India elements in that country.

Following Trudeau's allegations last year, India temporarily suspended issuance of visas to Canadian citizens. The visa services were resumed several weeks later.