India's official visa processor in Canada said Thursday it had been told to stop handling applications, before taking down the notice amid a diplomatic row sparked by Ottawa's accusation New Delhi was involved in the killing of a Sikh separatist.

Shortly after the announcement was splashed across Indian media, BLS removed the notice from their website. There was no immediate comment from India's foreign ministry.

An official at New Delhi-headquartered BLS said they did not want to be quoted and referred AFP to Indian authorities.

"Important notice from Indian Mission: Due to operational reasons, with effect from 21 September 2023, Indian visa services have been suspended till further notice," BLS International had posted on their website Thursday.

Canada's Prime Minister Justin Trudeau has demanded India treat with "utmost seriousness" allegations that Indian agents played a role in the June murder of Hardeep Singh Nijjar near Vancouver.

The fallout prompted tit-for-tat diplomatic expulsions and a forceful denial from India, which said any suggestion it played a role in Nijjar's killing was "absurd".

The suspension of visas comes a day after India's foreign ministry said it was concerned for the safety of its citizens in Canada because of "politically-condoned hate crimes and criminal violence".

"Threats have particularly targeted Indian diplomats and sections of the Indian community who oppose the anti-India agenda," a ministry statement said Wednesday.

"Indian nationals are therefore advised to avoid travelling to regions and potential venues in Canada that have seen such incidents."

The advisory did not name specific cities or locations for Indians to avoid.

Nijjar was shot dead by two masked assailants outside the Sikh temple he presided over in Surrey, an outer suburb of Vancouver.

An activist for the creation of a Sikh state known as Khalistan, Nijjar was wanted by Indian authorities for alleged terrorism and conspiracy to commit murder.

He had denied those charges, according to the World Sikh Organization of Canada, a nonprofit organisation that says it defends the interests of Canadian Sikhs.

The Indian government accuses Ottawa of turning a blind eye to the activities of radical Sikh nationalists who advocate the creation of an independent Sikh state to be carved out of northern India.