"I want to make a deal with Iran. I want to do something, if it's possible," Trump told a summit of Gulf Arab leaders in Riyadh.

"But for that to happen, it must stop sponsoring terror, halt its bloody proxy wars, and permanently and verifiably cease its pursuit of nuclear weapons.

"I'm strongly urging all nations to join us in fully and totally enforcing the sanctions that I just placed on Iran," he said.

It was unclear what he meant by "just placed" but the Trump administration in recent weeks has imposed sanctions on a series of entities and individuals linked to Iran's oil industry and nuclear programme.

In 2018, Trump walked out of a landmark agreement between major powers and Iran that gave it sanctions relief in return for UN-monitored restrictions on its nuclear activities.

He slapped sweeping sanctions on Iran, including secondary measures against any country that buys Iranian oil.

Trump said that such secondary sanctions "are in certain ways even more devastating" than direct sanctions on Iran.

The Trump administration has held four rounds of talks with Iran, as the president seeks to avert a threatened Israeli military strike on Tehran's nuclear programme.

Both the United States and Iran have said that the talks took place in a positive atmosphere but they have not appeared to have gone in depth on technical aspects of an accord.

Iran, which denies it is pursuing nuclear weapons, said it also expects to hold talks with Britain, France and Germany on Friday in Turkey.