President Donald Trump has been handing out his mobile phone number to world leaders and urging them to call him directly, an unusual invitation that breaks diplomatic protocol and is raising concerns about the security and secrecy of the U.S. commander in chief’s communications.

Trump has urged leaders of Canada and Mexico to reach his mobile phone, according to former and current U.S. officials with direct knowledge of the practice. Of the two, only Canadian Prime Minister Justin Trudeau has taken advantage of the offer so far, the officials said.

Trump also exchanged numbers with French President Emmanuel Macron when the two spoke immediately following Macron’s victory earlier this month, according to a French official, who would not comment on whether Macron intended to use the line.

All the officials demanded anonymity because they were not authorised to reveal the conversations. Neither the White House nor Trudeau’s office responded to requests for comment.