But on Wednesday the US President will wield the gavel in the United Nations Security Council to denounce Iran for what his administration sees as its malign regional behaviour.

Trump is set to preside over the 15-member council as the United States holds the monthly rotating presidency, which coincides with the annual gathering of world leaders at the United Nations in New York.

"I am sure that's going to be the most watched Security Council meeting ever," US Ambassador to the United Nations Nikki Haley told reporters.

But despite the unpredictable nature of Trump, some diplomats aren't expecting a reality television performance in the Security Council, where nearly every member is likely to be represented by their prime minister or president except Russia and China, which are expected to send ministers.

"I don't think it will be that entertaining at all," said one senior UN diplomat, speaking on condition of anonymity.

"Even those who don't like him, the attitude of all other heads of state and government in a public meeting when faced with any president of the United States of America is to be on their best behaviour," the diplomat said.

It is rare for the council - formed in 1945 to maintain international peace and security - to meet at the head-of-state and government level. This will be the third time the body is chaired by a US president. It has the ability to impose sanctions or authorise the use of military force.

Trump's predecessor Barack Obama presided over meetings in 2009 and 2014 on nuclear nonproliferation and foreign terrorist fighters. In both cases the council adopted resolutions on the topics under discussion. US Ambassador Nikki Haley said there are no plans to adopt a resolution at Wednesday's meeting.

"We want to make sure (Iran) understands the world is watching. That's the biggest reason for this meeting," she said earlier this month.

The topic of the meeting will be nonproliferation of weapons of mass destruction, a broad issue that allows leaders around the horse-shoe table to raise a variety of subjects from North Korea to chemical weapons attacks in Syria and Britain.

However, Trump signalled on Twitter he will zero in on Iran, when he posted: "I will chair a United Nations Security Council meeting on Iran." Tehran has accused the United States of abusing the power of the Security Council president.

Australian Associated Press