The European parties to the Iran nuclear deal -- Britain, France and Germany -- have been battling to save it since US President Donald Trump withdrew from it and reimposed tough sanctions on Tehran.

Iran has responded to the US pullout with a series of steps back from its own commitments under the deal, including by increasing uranium enrichment.

But Foreign Minister Mohammad Javad Zarif said the Islamic republic could be willing to move back towards compliance -- under certain circumstances.

"We have said that we are prepared to slow down or reverse these measures commensurate with what Europe does," Zarif told reporters at the Munich Security Conference.

"We will decide whether what Europe does is sufficient to slow down or to reverse some steps -- we have not even ruled out reversing some of the steps that we have taken."

Europe has set up a special trading mechanism called Instex to try to enable legitimate humanitarian trade with Iran to offset some of the effects of US sanctions.

But it has yet to complete any transactions and the Iranian side does not think it is sufficient.

"We're not talking about charity. We're talking about Iranian rights and the rights of the Iranian people to receive the economic benefits," Zarif said.

"We have received irreversible harm or irreparable harm because of US sanctions, but nevertheless we will reverse the steps that we have taken provided that Europe takes steps that are meaningful."

The EU's top diplomat Josep Borrell met Zarif in Tehran earlier this month to try to lower tensions after Britain, France and Germany triggered a complaint mechanism under the deal to try to press Tehran to return to full implementation.

Washington accuses Tehran of seeking a nuclear weapon, which Iran has always denied.

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.

Borrell has also been in consultation with the other countries still in the deal -- Russia and China -- who like their European counterparts want to save the accord.

A meeting of the joint commission that oversees the deal is due to be held this month to consider the dispute mechanism.