A handout photo provided by the Iranian presidency on Monday shows Iranian President Hassan Rouhani attending a farewell ceremony at the Mehrabad airport in Tehran, shortly before leaving Tehran for the UN General Assembly in New York. Photo: AFP

US President Donald Trump said on Monday he could not rule out a meeting with Iranian counterpart Hassan Rouhani at the United Nations this week, but no encounter was yet scheduled.

Speculation has been rife over whether the leaders of the two arch-foes would finally meet on the sidelines of the UN General Assembly in New York, with France's Emmanuel Macron trying to broker what would be a historic rendezvous.

The chances of this happening have seemingly diminished in the wake of a dramatic attack on Saudi oil facilities blamed by the US on Iran, which denies being involved.

"I never rule anything out," Trump told reporters, but added that he had "nothing scheduled at this moment."

Macron is cautiously hopeful for a breakthrough and is seeking to bring the two together, having consulted informally with Trump on Monday, then meeting for more than 90 minutes with Rouhani that evening.

"The path of de-escalation is narrow but more necessary than ever, and it was time for Iran to take it," Macron told Rouhani in the meeting, according to a statement from the French presidency.

Macron plans to meet with the US president again on Tuesday, and told reporters earlier on Monday, "I'll do everything I can so that conditions are created for discussion."

However Trump responded to his efforts by saying "we don't need a mediator." 

The Iranians "know whom to call," he said.

Tehran and Washington have been at loggerheads since May last year when Trump abandoned a 2015 nuclear deal and began reimposing sanctions on Iran in a campaign of "maximum pressure."