Canadian PM Justin Trudeau has reiterated that there are "credible reasons" to believe that Indian agents may have been behind the murder of a Sikh separatist on Canadian soil.

He first made the allegation on Monday, which India has strongly rejected, calling them "absurd".

Hardeep Singh Nijjar - who India designated a terrorist in 2020 - was shot dead outside a temple in June.

Tensions between the two countries have flared after the allegation.

The Indian government has often reacted sharply to demands by Sikh separatists in Western countries for Khalistan, or a separate Sikh homeland.

Though India designated Nijjar a terrorist, his supporters reject the claim, saying he was a peaceful activist who backed the demand for a separate homeland for Sikhs.

Mr Trudeau's accusation has fuelled an ugly diplomatic row between India and Canada, two countries that have historically shared close ties and good trade relations.

Both countries have expelled a diplomat each of the other nation and on Thursday, India suspended visa services for Canadians.

Meanwhile, Canada has reduced its personnel in India saying some diplomats had received threats on social media.

On Thursday, Mr Trudeau spoke to reporters in New York at the sidelines of the UN General Assembly and repeated some of his earlier claims.

"As I said on Monday, there are credible reasons to believe that agents of the government of India were involved in the killing of a Canadian on Canadian soil," he said and added that by doing so, the country is standing up for the "rules based international order that we believe in".

When asked by a reporter to characterise "how extensive and solid" the evidence was, Mr Trudeau didn't give a direct answer but said that Canada had a "rigorous and independent justice system" and "we allow those justice processes to unfold themselves with the utmost integrity".

He also said that the decision to share these allegation was not done lightly but with "the utmost seriousness".

When asked if Indian Prime Minister Narendra Modi had confirmed or denied these allegations, Mr Trudeau said he had had a "direct and frank conversation" with Mr Modi "in which I shared my concerns in no uncertain terms".

Mr Trudeau visited India earlier this month for the G20 summit during which he had a tense meeting with Mr Modi.

India had then issued a sharp statement saying that it had "strong concerns about continuing anti-India activities of extremist elements in Canada" who it accused of "promoting secessionism and inciting violence against Indian diplomats".

Mr Trudeau said Canada would always defend "freedom of expression" while acting against hatred.

Hours before Mr Trudeau spoke to the press on Thursday, Arindam Bagchi, a spokesperson for India's foreign ministry, told reporters that India had made it clear that "we are willing to look at any specific information that is provided to us. But so far we have not received any such specific information."

The UK, Australia and the US have expressed concern over Canada's allegations.

On Thursday, US National Security Advisor, Jake Sullivan, said that the US was consulting closely with its Canadian counterparts and has been in touch with the Indian government as well.

"I firmly reject the idea that there is a wedge between the US and Canada. We have deep concerns about the allegations, and we would like to see this investigation carried forward and the perpetrators held to account," he said.