UN has "tremendous potential", but is underutilised: Trump

The meeting between Trump and UN Secretary-General Antonio Guterres is expected to focus on Trump's reform agenda, the Iran nuclear deal, Middle East peace prospects and global extremism.

"I have to say the United Nations has tremendous potential. It hasn't been used over the years nearly as it should be," Trump told reporters as he met Guterres in his Oval Office.

"We have just started," he said, adding that the world body is "almost a power to bring people together" like nothing else.

"It hasn't been used. You are starting to really get your arms around it, and I have a feeling that things are going to happen with the United Nations like you haven't seen before," he said.

Trump praised Guterres for his efforts to reform the world body.

"I am a true believer that we live in a messy world, but we need strong reforms, a modernised UN, we need a strong United States engaged, based on its traditional values freedom, democracy, human rights, and we need a very solid cooperation between the US and the UN," Guterres said.

Trump said in September that the UN had not reached its potential because of "bureaucracy and mismanagement".

He had called upon the UN to change "business as usual and not be beholden to ways of the past which were not working".

He also suggested the US was paying more than its fair share for UN operations.