The remaining parties to the Iran nuclear deal will meet in Vienna on Wednesday, the EU's diplomatic service announced, after Britain, France and Germany launched a dispute process over Iran's successive pullbacks.

The office of EU diplomatic chief Josep Borrell -- who is tasked with convening the commission under the dispute mechanism -- said the get-together would be chaired on his behalf by senior official Helga Schmid.

The meeting comes as the European parties try to find a way to persuade Iran to come back into line with the deal after Tehran made a series of steps away in protest at the US pulling out and reimposing sanctions.

The 2015 agreement to curb Iran's nuclear programme in return for sanctions relief has been slowly crumbling since US President Donald Trump unilaterally withdrew in 2018, describing the accord signed by his predecessor Barack Obama as a bad deal.

The EU has led efforts to try to save the deal, arguing that it is vital for international security, but after repeated warnings over Iran's moves, Germany, Britain and France triggered the dispute process on January 14.

In its last announcement, Tehran said it would no longer observe limits on the number of centrifuges used to enrich uranium. It was its fifth step away from the deal since Trump's pullout. Borrell has said he believes all the countries still in the deal -- which also include Russia and China -- are determined to save the accord.

Iran looking for concessions

Western diplomats recognise it is highly unlikely Iran will heed calls to come back into full compliance without substantial concessions in return -- such as an end to US sanctions or Europe taking measures to offset their economic impact.

Instead they hope to use the dispute process, which can be strung out for quite some time, to convince Iran not to take any more moves away from the deal, giving space for back-channel diplomacy aimed at bringing Washington and Tehran back into alignment. At a major international security conference in Munich earlier this month, Iran's Foreign Minister Mohammad Javad Zarif said Tehran would be prepared to move back towards the deal if Europe provides "meaningful" economic benefits.

Crucially, Iran has said it will continue to cooperate with the Vienna-based International Atomic Energy Agency (IAEA) which carries out regular detailed inspections on the ground. Europe has set up a special trading mechanism called Instex to try to enable legitimate humanitarian trade with Iran, but it has yet to complete any transactions and Tehran regards it as inadequate.

The renewed US sanctions have almost entirely isolated Iran from the international financial system, driven away oil buyers and plunged the country into a severe recession.