Washington, Sep 26 : The US has reiterated that it was "deeply concerned" by the allegations levelled by Canadian Prime Minister Justin Trudeau over the involvement of officials of Indian agencies in the murder case of Canada-based pro-Khalistan hardliner Hardeep Singh Nijjar. Replying to a query during a regular press briefing on Monday, spokesman for the US State Department Matthew Miller said: "We remain in close contact with our Canadian partners, as the Secretary (Antony Blinken) said on Friday (September 22). We believe it's critical that Canada's investigation proceed and that the perpetrators be brought to justice. "And we have publicly ' and privately ' urged the Indian government to cooperate in the Canadian investigation." The spokesman's remarks came days afterBlinken urged India to cooperate with Canada and ensure "accountability" over Nijjar's killing on June 18 outside a Sikh temple in British Columbia. Speaking to reporters on the sidelines of the UN General Assembly on September 22, Blinken said the US has been in touch both with India, with which it has warming ties, and Canada, a close ally. The Secretary of State also indicated that the US was playing more an a passive, observer's role. "We have been consulting throughout very closely with our Canadian colleagues ' and not just consulting, coordinating with them ' on this issue. "And from our perspective, it is critical that the Canadian investigation proceed, and it would be important that India work with the Canadians on this investigation. We want to see accountability, and it's important that the investigation run its course and lead to that result," he added, Trudeau's accusation has led to a diplomatic spat between India and Canada with New Delhi rejecting Ottawa's claims as "absurd and motivated", followed by tit-for-tat expulsions of senior diplomats and travel advisories. /IANS