The Prime Minister's Office says it is not aware of any telephone conversation between Justin Trudeau and Donald Trump on the U.S. president's private cellphone.

An Associated Press report this week said Trump has been handing out his cellphone number to world leaders and urging them to call him directly. The unusual invitation breaks diplomatic protocol, and has raised concerns about the security and secrecy of the U.S. commander in chief's communications, according to the report.

Citing unnamed former and current U.S. officials with direct knowledge of the practice, the report said Trump urged leaders of Canada and Mexico to reach him on his cellphone. The report also said of the two, only Trudeau had taken advantage of the offer so far.

French President Emmanuel Macron also exchanged mobile numbers with Trump, according to the AP report, but it was not known if he intended to use it.

An official in the PMO would not say if Trump had given Trudeau his mobile number, but said the office does not know of any call between the two leaders conducted on a cellphone.

"As far as we can tell, as far as we are aware, none of these conversations have taken place on a cellphone," the official said.

The two world leaders spoke by phone Thursday. A readout of the call said Trudeau "expressed his disappointment" with Trump's decision to withdraw from the Paris Agreement on Climate Change.

The last time the pair spoke by phone was April 26 on trade relations, though they met in person at the NATO and G7 summits in Europe this month. The Privy Council Office, the bureaucratic department for the prime minister, said Trudeau has spoken with Trump by telephone on seven occasions before yesterday, and each one has been publicly reported.

Those calls took place between Nov. 9, 2016, and April 26, 2017, ranging in topics from congratulations on Trump's election to condolences from the U.S. to Canada for the mosque shooting.

Other topics included softwood lumber and other trade issues, as well as chemical weapons attacks in Syria.

Readouts publicly posted

"Every time the prime minister has spoken with President Trump, media have been made aware through readouts published on our website," Paul Duchesne, a spokesman for the Privy Council Office, told CBC News.

Presidents have traditionally placed calls on secure phone lines.

The PMO declined to discuss protocol for leader-to-leader phone calls.

Andrew MacDougall, former communications director for Stephen Harper, said PCO would have secure communications for the prime minister whether he was in his office, at the residence, or travelling.

Calls were arranged by senior officials in advance, with each leader connected through a switchboard on a secure line.

"It was very much a formal process," he said.

Security top priority

MacDougall said security was always a top priority, and staff would not even bring BlackBerry devices into meetings to avoid breaches.

Trump hammered Democratic rival Hillary Clinton during the presidential campaign for using a private email server while she was secretary of state because he said it could compromise the security of classified information.