NUCLEAR negotiators yesterday failed to meet a deadline for a deal over Iran’s atomic programme.

Diplomats at the talks in Vienna said that it had been agreed to extend negotiations for a comprehensive agreement until July 2015.

“Experts and negotiating teams are reconvening in December at a yet-to-be-determined location,” a Western diplomat said.

Under the terms of limited agreements reached after six frenetic days of talks, a political accord is to be completed by March 1, with final details contained in annexes to be sealed by July 1, the diplomats claimed.

Iran, Germany and the five permanent members of the UN security council — China, France, Russia, Britain and the US — had set a deadline of midnight to come to a final agreement on a mechanism whereby Iran’s pathways to develop a nuclear weapon would be closed in return for relief from international sanctions.

But British Foreign Secretary Philip Hammond said that it “was not possible to meet the deadline” due to wide gaps on well-known points of contention, including levels of uranium enrichment and the number of centrifuges that Iran would operate.

He stressed that, while July 1 was the new deadline for a comprehensive deal, the expectation was that broad agreement would be in place by March 1.

In the interim, expert-level talks would resume in December at an as yet undetermined venue and Iran would receive about £446 million per month in frozen assets, Mr Hammond said.

US Secretary of State John Kerry and Iranian Foreign Minister Mohammad Javad Zarif agreed on Sunday to start discussion on the extension as it became clear that it would be almost impossible to bridge the differences between them in the time remaining before the deadline.

Chinese Foreign Minister Wang Yi said that negotiators were still having “consultations” on a final agreement to meet both US demands for strict curbs on Tehran’s nuclear programme and Iran’s insistence on sanctions relief.

Mr Wang arrived at the Vienna talks yesterday, joining the foreign ministers of the other negotiating countries in a top-level diplomatic effort to push the talks forward.