Pope Leo lamented on Friday the frictions roiling relations between the United States and Canada, in a likely reference to US President Donald Trump's decision to cut off US-Canada trade talks.

"Canada and the United States ... as we are sitting here, are experiencing great difficulties," Leo, the first US pope, told a meeting at the Vatican.

"Two countries that were once considered the closest allies at times have become separated from one another," he said.

It is unusual for the leader of the 1.4 billion-member Catholic Church to comment on matters of international trade, or on politics in any individual country.

Leo has not spoken previously about Trump's trade policies, but has been ramping up disapproval of the Trump administration's treatment of migrants, drawing a heated backlash from some prominent conservative Catholics.

The pope was responding on Friday to a question from a Canadian bishop during an event focused on possible reforms for the global Church, which are being discussed over a years-long process of dialogue.

Leo suggested that process, called a synod, could have lessons for the US and Canada.

"It's another proof ... of why synodality, listening, and dialogue are so important and how they have concrete applications in our daily lives," he said.