India has reacted angrily after being told by Canada that its ambassador and other diplomats were named as “persons of interest” in an investigation in the country.

The foreign ministry in Delhi said it received the news in a diplomatic communication from Canada on Sunday, and reserved the right to respond. “The Government of India strongly rejects these preposterous imputations,” it said.

The statement refers to allegations last year by Canadian Prime Minister Justin Trudeau that the Indian government may have been behind the killing of a Sikh separatist on Canadian soil. Delhi has repeatedly rejected the allegation.

The row led to a deterioration in ties, with India asking Canada to withdraw dozens of its diplomatic staff and suspending visa services.

On Monday, India’s foreign ministry said Canada’s allegations were part of Trudeau’s “political agenda” and warned of action, without specifying what it would be.

“India now reserves the right to take further steps in response to these latest efforts of the Canadian Government to concoct allegations against Indian diplomats,” it said.

Delhi also defended its High Commissioner Sanjay Kumar Verma, referring to his “distinguished career spanning 36 years”.

“The aspersions cast on him by the Government of Canada are ludicrous and deserve to be treated with contempt,” it said.

There was no immediate Canadian response to Delhi’s statement.

Hardeep Singh Nijjar was shot and killed in June 2023 by two masked gunmen outside a Sikh temple he led in Surrey, British Columbia.

He had been a vocal supporter of the Khalistan movement, which demands a separate Sikh homeland, and publicly campaigned for it.

India has in the past described him as a terrorist who led a militant separatist group – accusations his supporters called unfounded.

Canadian police called his killing a “targeted attack”.

In September 2023, Trudeau had told Canada’s parliament that allegations of Indian involvement in the killing were based on Canadian intelligence.

He called the act a violation of Canada’s sovereignty.

India has vehemently denied all allegations and maintained that Canada has provided no evidence to support its claims.

Frosty ties between the two countries seemed to have thawed slightly after India resumed processing visas in October 2023.

But last week, Canadian Foreign Minister Mélanie Joly called the country’s relations with India “tense” and “very difficult”.

She also said there remained a threat of more killings like Nijjar’s on Canadian soil.