US President Donald Trump wielded the gavel in the United Nations Security Council Wednesday to denounce Iran for what his administration sees as its malign regional behavior.

Trump said the Syrian regime's "butchery" is enabled by Russia and Iran.

He also told the council that the US will pursue tougher sanctions against Iran and that the US will work to ensure that Iran never acquires a nuclear bomb.

Trump and Iranian President Hassan Rouhani exchanged taunts at the assembly session, with Trump threatening more sanctions against Tehran and Rouhani suggesting the U.S. president suffered from a "weakness of intellect".

The President also accused China of seeking to meddle in the November 6 US congressional elections on Wednesday, saying Beijing did not want his Republican Party to do well because of his stance on trade.

"China has been attempting to interfere in our upcoming 2018 election, coming up in November. Against my administration," Trump told a UN Security Council meeting whose ostensible subject was on nonproliferation of weapons of mass destruction and Iran.

Trump did not provide any evidence for the allegation. China did not immediately respond to the remarks by Trump, who was chairing the Council meeting.

"They do not want me or us to win because I am the first president ever to challenge China on trade and we are winning on trade, we are winning at every level. We don't want them to meddle or interfere in our upcoming election," Trump said.

Trump himself is not up for re-election until 2020 but November's voting will decide whether his Republican party can keep control of the US House of Representatives and the Senate.