A former member of a Sikh "terrorist" group was invited to a formal dinner in New Delhi alongside Canada's Justin Trudeau, an invitation the Canadian prime minister said was "immediately rescinded" once it came to his attention.

Jaspal Atwal should never have received an invitation to the event, Trudeau told reporters in New Delhi on Thursday, after the incident garnered widespread media attention in both India and Canada.

"Obviously we take this situation extremely seriously. The individual in question never should have received an invitation and as soon as we found out, we rescinded the invitation immediately," Trudeau said.

He said a Canadian parliament member "will assume full responsibility" for the invitation, which was extended to Atwal for a dinner organised by the Canadian High Commissioner in New Delhi in honour of Trudeau's visit.

Atwal is a former member of the International Sikh Youth Federation, which supports the creation of an independent Sikh state in India's Punjab province, Canadian media reported.

The Canadian government lists the organisation as a "terrorist entity".

Atwal was also convicted of attempted murder of an Indian cabinet minister in the Canadian province of British Columbia in 1986, CBC News said.

Support for 'united India'

Tensions over Canada's alleged support for Sikh separatism have dominated the Canadian prime minister's first official trip to India.

Earlier this week, Trudeau rejected allegations that members of his government support the Sikh separatist movement known as Khalistani.

Trudeau on Thursday "conveyed his support for a united India" during a meeting with the chief minister of Punjab, Amarinder Singh.

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Singh, for his part, welcomed Trudeau's "categorical assurance ... that his country does not support any separatist movement".

Meanwhile, India's Ministry of External Affairs said it was looking into how Atwal was granted a visa to come to India in the first place.

The "Canadian side has already clarified that the invitation has been withdrawn. Let us not presume things and decide how he managed to come," said Raveesh Kumar, a ministry spokesman, the Times of India reported.

Atwal is no longer on an Indian government's blacklist of suspected Sikh extremists, the newspaper said.

Trudeau is expected to meet Indian Prime Minister Narendra Modi on Friday, Canadian media reported, a day before his visit formally concludes.