Prime Minister Justin Trudeau says he went to the Aga Khan's private island in the Bahamas at Christmas in 2014, when he was an MP and leader of the Liberal Party, travelling there on the wealthy philanthropist's private helicopter.

Trudeau made the remarks in response to a reporter's question at the closing news conference of the Liberal caucus retreat in Calgary, explaining the two men have been family friends since Trudeau was a child.

"The first time I went on vacation with the Aga Khan I was 12 years old," Trudeau said. "It was a family trip with my father and my brothers and we had a wonderful time in Greece with him there.

"I have seen him many times since then for dinners at his place, I've been at various places around the world, and yes, in Christmas of 2014 I spent some time with him on Bell Island as well."

Asked if he was taken there by the Aga Khan's private helicopter, Trudeau replied "yes."

The Aga Khan is the Imam and spiritual leader of the world's approximately 15 million Ismaili Muslims who believe he is the direct descendant of Islam's Prophet Muhammad.

He is also the founder and head of the Aga Khan Development Network, which engages in charitable development work in some of the poorest parts of the world. The organization receives some of its funding from the federal government.

Trudeau has come under criticism ever since the National Post first reported that he and his family stayed at the Aga Khan's Bell Island home in the Bahamas for a post-Christmas vacation, also travelling there in the spiritual leader's private helicopter.

Also on the trip were Liberal MP Seamus O'Regan, his husband Steve Dousis, Liberal Party president Anna Gainey and her husband Tom Pitfield.

A question of ethics

Canada's Ethics Commissioner Mary Dawson is currently investigating Trudeau's most recent trip to the island, and his use of the Aga Khan's private helicopter to get there, to determine if it violated the Conflict of Interest Act.

Dawson is looking into whether Trudeau's trip violated sections 6, 11, 12 or 21 of the Act.

Section 11 of the Conflict of Interest Act prohibits office holders from accepting gifts that might be seen to influence them in an official power, duty or function, unless the gift is part of protocol or is from a relative or friend.

Section 12 bars ministers from accepting travel on private aircraft unless it is required in his or her capacity as a public office holder or in exceptional circumstances or with prior approval of the commissioner.

Ethics Commissioner Mary Dawson is investigating Trudeau's recent post-Christmas trip to the Aga Khan's private island. (Adrian Wyld/Canadian Press)

Sections 6 and 21 require public office holders to recuse themselves from discussion, decision, debate or vote on any matter in which they may be in conflict of interest.

The prime minister's own Open and Accountable Government guidelines, issued shortly after he took office in 2015, also restrict sponsored travel unless it is "exceptional circumstances and only with the prior approval" of the ethics commissioner.

The maximum penalty Trudeau could face is a "notice of violation," though a finding of a breach of the act would give the opposition ammunition to question Trudeau's commitment to transparency and ethical conduct.

The Office of the Conflict of Interest and Ethics Commissioner of Canada was established in 2007 under then prime minister Stephen Harper.

Trudeau was subject to different conflict of interest rules as an opposition MP when he travelled by helicopter to Bell Island in 2014. The Conflict of Interest Code bars an MP from accepting gifts or benefits "that might reasonably be seen to have been given to influence the member in the exercise of a duty or function of his or her office."

Trudeau did not declare the 2014 trip as sponsored travel, according to documents on the Ethics Commissioner's website. Under a separate rule, MPs are only required to declare sponsored travel worth more than $200 that "arises from or relates to his or her position."

Trudeau has insisted his visits to Bell Island, which can only be reached by private aircraft or by water, were personal in nature because the Aga Khan is a long-time family friend.