Rubio, who had a private audience with the pope on Thursday, told reporters they discussed areas of joint interest, including religious freedom and the threat posed by Iran.

"It's important to share our points of view and an explanation and an understanding of where we're coming from. And I thought it was very positive," he said.

Rubio's visit came after Trump accused Leo, head of the world's 1.4 billion Catholics, of being "weak on crime and terrible for foreign policy" after he made critical comments about the Middle East war.

"We had a very good meeting," said Rubio, who also met with Vatican Secretary of State Pietro Parolin.

"I updated them on the situation with Iran, expressed our point of view about why this is important, and the danger that Iran poses to the world," he said.

It was also an "opportunity to personally express my feelings", he said.

The US diplomat, a devout Catholic, had earlier sought to play down the rift between Trump and the pope, which sparked global headlines and risked alienating Catholic US voters.

"This is a trip that had been planned even before all these things had happened," he said Friday.