A former CSIS director and national security adviser to two prime ministers says he’s not surprised India may have been involved in some foreign interference activities in Canada.

On Monday afternoon, Trudeau told the House of Commons in a rare statement on a matter of national security that Canadian intelligence agencies were investigating "credible allegations" that agents of the Indian government were involved in the June death of prominent Canadian Sikh leader Hardeep Singh Nijjar in B.C.

Trudeau stood by the intelligence Tuesday, despite New Delhi calling the claim "absurd."

“Was I surprised that India might have been involved in some act of foreign interference? No. That it was involved in extra-judicial killing? Yes,†said Richard Fadden, who served as national security adviser to Trudeau and former prime minister Stephen Harper.

He said the Indian government has been “mucking about†in Canada’s affairs for quite a while now, and various governments “have done a variety of things, but clearly not enough, to stop them.â€

“And I still don't think that we're taking it seriously given the breadth of activity that really puts our sovereignty at risk,†he said.

While some of Canada’s allies have issued statements calling for a fulsome investigation into Nijjar’s killing, some foreign affairs and intelligence experts said a hesitance to be more vocal could be attributed to the delicate diplomatic balancing act that is necessary given India's strategic and economic importance in the world.

"We are deeply concerned about the allegations referenced by PM Trudeau yesterday," said a U.S. State Department spokesperson in a comment to CTV News. "We remain in regular contact with our Canadian partners. It is critical that Canada’s investigation proceed and the perpetrators be brought to justice."

Meanwhile, U.S. National Security Council spokesperson John Kirby told CNN in an interview Tuesday the allegations that agents of the Indian government were involved should be investigated to determine their credibility before officials formulate a response.

"We believe in order to determine how credible they are, there needs to be a thorough, transparent, comprehensive investigation,†Kirby said. “Prime Minister Trudeau has called for that investigation, so we are going to watch and see how Canada moves forward on this.â€

Kirby added the U.S. government is urging India to co-operate in the investigation.

Vincent Rigby, a former national security adviser, said the matter “really does complicate†relations between Canada and India, which have been allies for a long time.

“I think we normally think of hostile state actors as China, as Russia, as Iran, as North Korea. So here's a country that is a democracy, is a partner in many respects to Canada, a fellow Commonwealth country that is maybe not a hostile state actor per se, but these are not benign activities. These are hostile activities, if indeed, they were carried out by the government of India,†he said.

When asked whether he takes anything from Canada’s allies questioning the credibility of the allegations, Fadden said “not really.â€

“Each country is going to pursue its own interest, broader interests, not just intelligence but economic political, and other,†he said, adding Canada has been dealing with both the criminal and political aspects of the investigation into Nijjar’s killing for “quite a while now.â€

“So I think it's not an unreasonable response,†he said. “Having said that, if we don't get our allies to support this, either publicly or privately, Canada's not going to be able to do a great deal to move India. And I think the greatest thing we can aspire to in the short term or the medium term is to get India not to do this again.â€

With files from CTV News Senior Digital Parliamentary Reporter Rachel Aiello and CTV News’ Annie Bergeron-Oliver