Trump has said that if the deal between Iran and six big powers, which curtailed Iran's nuclear programme in exchange for sanctions relief, is not "improved" by then, he will withdraw.

In particular Trump says that the "terrible" agreement does not address Iran's ballistic missile programme or Tehran's activities in the Middle East.

In addition, parts of the agreement are due to start expiring in the mid-2020s.

Iran, which according to the UN atomic watchdog has been abiding by the deal since it came into force in January 2016, has ruled out any changes to the agreement.

The talks in Vienna on Friday, a regular review of the accord, involved Iran, senior US official Brian Hook and representatives of Russia, China, France, Britain and Germany.

According to US officials, Hook was in Berlin on Thursday to meet British, French and German counterparts to try and agree a common line.

The European parties to the agreement are desperate to save it and have been scrambling to find ways to persuade Trump not to rip it up.

"We share all the concerns with the missiles, with the regional destabilisation, with the support to terrorism, with the malign activities of Iran," one European diplomat said.

"We are ready to take steps to address these concerns."

But he added: "We need to make sure that we don't throw out the baby with the bath water, so we keep the nuclear agreement and we act on the rest in parallel... Disregarding the JCPOA (the deal) would put us in the worst place to address the other concerns."

Trump's decision this week to replace Rex Tillerson with Mike Pompeo as secretary of state has been widely seen as another bad omen for the agreement.

Tillerson and his erstwhile cabinet ally Defence Secretary Jim Mattis had urged Trump to listen to the Europeans to preserve the agreement.

Pompeo, head of the Central Intelligence Agency, is known to take a much harder line.

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