A woman walks in front of a mural painting depicting the Iranian flag, in the capital Tehran on August 6, 2018 as Iran is bracing for the return of US sanctions. (Photo: AFP)

Iran said the United States was "isolated" in its hostility to the Islamic republic on Monday, as it braced for the return of sanctions against a backdrop of political turmoil inside the country.

"Of course, American bullying and political pressures may cause some disruption, but the fact is that in the current world, America is isolated," Foreign Minister Mohammad Javad Zarif told reporters, according to the semi-official ISNA news agency.

Washington is set to reimpose sanctions on Iran on Tuesday following President Donald Trump's decision to abandon the 2015 nuclear deal in May -- a move opposed by all other parties to the agreement.

"We deeply regret the re-imposition of sanctions by the US," said EU diplomatic chief Federica Mogherini in a statement jointly signed with the foreign ministers of Britain, France and Germany.

"We are determined to protect European economic operators engaged in legitimate business with Iran," the statement added.

Sanctions are due to return in two phases on August 7 and November 5 -- with the first targeting Iran's access to US banknotes and key industries including cars and carpets.

The second phase -- blocking Iran's oil sales -- is due to cause more damage.

After months of fierce rhetoric, Trump surprised observers last week when he offered to meet with Rouhani without preconditions.

But Zarif suggested it was hard to imagine negotiating with the man who tore up an agreement on which Iran and world powers had spent the "longest hours in negotiating history".

"Do you think this person (Trump) is a good and suitable person to negotiate with? Or is he just showing off?" he said.

There have been ongoing rumours that Trump and Rouhani could meet in New York later this month, where they are both attending the UN General Assembly -- though Rouhani reportedly rejected US overtures for a meeting at last year's event.

Over the weekend Trump once again floated the idea of meeting, tweeting "I will meet, or not meet, it doesn't matter -- it is up to them!"

But that came less than a fortnight after a bellicose exchange between the two presidents, with Rouhani warning of the "mother of all wars" and Trump responding with a Twitter tirade against Iran's "DEMENTED WORDS OF VIOLENCE".

Trump has stated he wants a new deal with Iran that goes beyond curbing its nuclear programme, and ends what America calls its "malign influence" in the region.