Trump brags about causing Iran 'turmoil' after ending nuclear deal

US President Donald Trump asserted on Monday that "nationwide riots" in Iran were triggered by the economic damage caused by Washington's sanctions on Tehran.

Trump, interviewed after his summit in Helsinki with President Vladimir Putin, said that Russia still supported the nuclear accord because it does business with the regime in Tehran, so the deal is in Moscow's interest.

"It is not good for us or for the world, but they have riots in all their cities," Trump told Fox News.

"The inflation is rampant, going through the roof. And not that you want to hurt anybody, but that regime wouldn't let the people know that we are behind them 100 percent.

"They are having big protests all over the country, probably as big as they have ever had before. And battles happened since I terminated that deal, so we will see," he added.

Most US allies have spoken in favour of keeping the nuclear deal intact, since in May Trump pulled the US out of the accord that was agreed between Tehran and world powers in 2015.

US sanctions were reimposed on Iran, effectively barring many multinational firms from doing business with Tehran.

Iran has remained defiant in the face of the US move, saying it has left the Trump administration internationally isolated.

"The illegal logic of the United States is not supported by any of the international organisations," President Hassan Rouhani said at the weekend.

Iran has faced mounting economic woes since the US withdrawal from the accord, with inflation rising sharply.

Its currency has plunged almost 50 percent in value over the past six months against the US dollar, prompting a rare strike earlier this month by traders in Tehran's Grand Bazaar.

There have also been reports of brief scuffles and small-scale protests in recent weeks although not of mass demonstrations.