The US State Department is reportedly struggling to keep Donald Trump on message during calls with foreign leaders.

It came as the US president was alleged to have veered off topic during a diplomatic exchange with French President François Hollande.

The former real-estate mogul fixated on his personal beliefs that China, Nato and other international organisations were a drain on the US, a senior government official told the Politico website.

“It was a difficult conversation, because he talks like he’s speaking publicly,” the source said. "It's not the usual way heads of state speak to each other. He speaks with slogans and the conversation was not completely organised.”

It would not be the first time Mr Trump has been accused of breaking with long-established foreign policy protocol.

Within weeks of winning the presidency, he spoke directly with Taiwan’s president, breaking a foundation of US-China relations: American support for the "One China" policy. China considers Taiwan to be a breakaway province, not an independent state free to talk to the wider international community.

Mr Trump also raised anxiety levels in the international community when he warned Mexican President Enrique Peña Nieto that the US would be prepared to send troops to the country to clear out the "bad hombres down there”.

Lessons in eloquence with Obama and Trump

He was also alleged to have put the phone down on Australian Prime Minister Malcolm Turnbull, after the pair argued over an agreement brokered by his predecessor Barack Obama to resettle refugees from an Australian camp.

Mr Trump was said to have called it the “worst call yet”, a claim both camps have denied.

Following the call with Mr Hollande, a statement from the White House said the President had "reaffirmed the US commitment to Nato and noted the importance of all Nato Allies sharing the burden on defence spending.

"The leaders also lauded our combined efforts to eliminate ISIS in Iraq and Syria."

A National Security Council member also refuted the senior official’s claims saying: “This is mischaracterisation due to the nature of the call. They did discuss the issue of countries meeting their defence commitments under Nato. They agreed that was important that countries meet their goals."

Senior democrats have expressed dismay at the exchanges and criticised Mr Trump's "Twitter diplomacy".

Following Mr Trump's conversations with the leaders of Mexico and Australia, Democratic Senator Mark Warner said: “This is not the way you lead our country”

An exchange with New Zealand Prime Minister Bill English reportedly went smoothly due to his thanking the president for taking the time to talk during the Super Bowl and speaking amicably about New Zealand golfer Bob Charles.