The move gives the European members more time to 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 in 2018.

Josep Borrell, the EU's diplomatic chief who is tasked with convening meetings under the dispute mechanism triggered last week, said he had consulted the countries still in the deal -- which also include China and Russia.

All are determined to save the accord, Borrell said, though it has been crumbling since President Donald Trump unilaterally withdrew and reimposed swingeing sanctions on Tehran, prompting the Islamic republic to announce a series of steps away from its commitments under the deal.

"Notwithstanding differences on modalities, there is agreement that more time is needed due to the complexity of the issues involved. The timeline is therefore extended," Borrell said in a statement.

"All agreed to pursue expert-level discussions addressing the concerns regarding nuclear implementation, as well as the wider impacts of the withdrawal of the United States from the JCPOA and its re-imposition of sanctions."

JCPOA is an acronym for the deal's formal title, the Joint Comprehensive Plan of Action.

Borrell said the so-called joint commission that oversees the deal and comprises representatives of all the countries involved will meet in February, though he did not give a precise date. It usually meets in Vienna, though it can also meet in New York or Geneva.