The US has termed Canadian PM Justin Trudeau's allegation about India's involvement in the killing of Khalistani leader Hardeep Singh Nijjar as 'very serious'.

He said the US supports Canada's move to investigate the issue and urged India to cooperate.

US National Security Council (NSC) Coordinator for Strategic Communications John Kirby told CNN: "We believe a fully transparent comprehensive investigation is the right approach so that we can all know exactly what happened."

"We encourage India to cooperate with that," he said.

US envoy to India also sought New Delhi's cooperation with Canada in investigating the incident.

Eric Garcetti was quoted as saying by ANI: "Those who are responsible must be held accountable. We hope that traditional friends and partners will cooperate in getting to the bottom of it."

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Relationship between India and Canada touched a new low after Prime Minister Justin Trudeau alleged New Delhi's involvement in the killing of the Khalistani leader.

Trudeau alleged that there are “credible allegations of a potential link” between Indian government agents and the killing of Khalistani leader Hardeep Singh Nijjar in Surrey in the British Columbia state of Canada in June.

Soon after Trudeau levelled the allegations against the Indian government in the country's Parliament, Canada’s foreign minister Mélanie Joly announced the expulsion of a “top Indian diplomat” as a consequence.

In a measure against Canada's actions, India also sacked a Canadian diplomat and asked him to leave the country within the next five days.

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India rejected the allegations made by Canada over the killing of Khalistani leader Hardeep Singh Nijjar.

"Similar allegations were made by the Canadian Prime Minister to our Prime Minister and were completely rejected," read the statement issued by the MEA.

Who was Hardeep Singh Nijjar?

Hardeep Singh Nijjar, a Canada-based pro-Khalistan leader, was shot dead in Surrey city, British Columbia province in June.

He had been a leading figure in the Khalistan separatist movement and was closely associated with Sikhs for Justice (SFJ).

Nijjar was also serving as the president of Guru Nanak Sikh Gurdwara in Surrey.

Nijjar, a member of the Khalistan Tiger Force (KTF), was a ‘wanted terrorist’ for his involvement in various acts of violence and subversive activities.