"It's possible, anything is possible," Trump told reporters in the Oval Office when asked about the possibility of a face-to-face with Rouhani during the gathering later this month.

"We'll see what happens with Iran. Whether they want to talk or not, that's up to them, not up to me," said the US leader, who decided in May to pull out of the 2015 nuclear deal between world powers and Iran.

"Iran is a much different place than when I took over the presidency," Trump added, describing the country as "in turmoil."

"When I took office it was just a question of how long until they took over the entire Middle East. Now they are just worrying about their own survival as a country."

Trump is due to lead September 26 meeting of heads of state of the UN Security Council, with the goal of ramping up pressure on Tehran over its alleged violations of council resolutions.