Ottawa (AFP) - Canada's ethics commissioner has opened a probe of Prime Minister Justin Trudeau over his lavish post-Christmas vacation at the private island of billionaire philanthropist and spiritual leader the Aga Khan.

In a letter to an opposition Conservative member of Parliament shown to AFP on Monday, Commissioner Mary Dawson said she was investigating whether Trudeau breached ethics laws in receiving a free Bahamas vacation and in using the Aga Khan's helicopter to fly to his private island.

Trudeau and his family, as well as a Liberal MP and the president of the party and their spouses, stayed at the Aga Khan's home on Bell Island in the Bahamas for a post-Christmas vacation.

The Aga Khan's foundation has received hundreds of millions of dollars from the Canadian government to promote development and other projects in several countries. It is registered as a lobbyist.

Canadian conflict of interest laws prohibit officeholders from accepting gifts. Free travel is specifically listed as prohibited for ministers.

Trudeau last week addressed the controversy after the opposition complained to Dawson, saying, "This was a personal family vacation."

The Aga Khan is a longtime friend of the Trudeau family, he added.

On a cross-Canada tour to bolster support for his leadership and his Liberal Party, Trudeau told reporters Monday, "I've heard from a number of people across the country that they're concerned about this, and that's why I take this very seriously." He said he would happily respond to questions from the ethics commissioner and others.

No Canadian prime minister has ever been found in breach of a federal statute, and even if Trudeau is found guilty of such a breach, the sanctions would be effectively a slap on the wrist.

The political fallout, however, is likely to be much worse for Trudeau, who rose to power in 2015 on a platform of openness and ethical conduct.