There are "credible allegations" linking India's government to the assassination of a Canadian citizen and prominent Sikh leader, Canadian Prime Minister Justin Trudeau alleged on Monday.

"Over the past number of weeks, Canadian security agencies have been actively pursuing credible allegations of a potential link between agents of the government of India and the killing of a Canadian citizen Hardeep Singh Nijjar," said Trudeau, adding his government would take all steps necessary '"to hold perpetrators of this murder to account."

Nijjar was a prominent Sikh leader in British Columbia, and according to local police, he was gunned down in his truck in June by two masked gunmen outside a Sikh temple in Surrey, BC.

His death both shocked and outraged the large Sikh community in Canada that now numbers in the hundreds of thousands.

India designated Niijar a terrorist threat several years ago, labeling him part of a separatist movement for Sikhism.

"Canada has declared its deep concerns to the top intelligence and security officials of the Indian government. Last week, at the G20, I brought them personally and directly to Prime Minister Modi in no uncertain terms. any involvement of a foreign government in the killing of a Canadian citizen on Canadian soil is an unacceptable violation of our sovereignty," said Trudeau during his speech in parliament, saying this was an 'extremely serious matter.'

Canadian police have not arrested anyone in connection with Niijar's murder, but in an August update, police released a statement saying they were now investigating three possible suspects and issued a description of a possible getaway vehicle, asking for the public's help.

CNN has reached out to the High Commission of India in Ottawa for comment but has not received a reply.