Talks on Iran's nuclear programme will continue until at least Thursday morning, two days after the original deadline, the US says.

US Secretary of State John Kerry has extended his stay to continue negotiations, officials say.

However, a number of foreign ministers have left the talks and China warned compromise was essential, otherwise "all previous efforts will be wasted".

A deal would curb the nuclear programme in return for sanctions relief.

Negotiations between the so-called P5+1 - the US, UK, France, China and Russia plus Germany - and Iran continued on Wednesday at Lausanne's Beau-Rivage Palace hotel after overrunning the self-imposed deadline of 31 March to reach a deal.

On Wednesday evening, a US state department spokeswoman said: "We continue to make progress, but have not reached a political understanding. Therefore, Secretary Kerry will remain in Lausanne until at least Thursday morning to continue the negotiations."

The P5+1 deal seeks to ensure Iran could not assemble a nuclear weapon in less than a year. The Iranians insist that they have no such ambition.
'Fingers crossed'

Earlier, UK Foreign Secretary Philip Hammond told the BBC: "I think we have a broad framework of understanding, but there are still some key issues that have to be worked through.

"Some of them are quite detailed and technical so there is still quite a lot of work to do but we are on it now and we'll keep going at it.

Mr Hammond stressed again that he would not sign up to a "bad deal".

Russian Foreign Minister Sergei Lavrov said earlier that "one can say with relative certainty that we at the minister level have reached an agreement in principle on all key aspects of the final settlement of this issue". He has now left the talks.

Iranian Foreign Minister Mohammad Javad Zarif said that "quite a bit" had been accomplished.

He and Mr Kerry held bilateral talks on Wednesday.

However, Deputy Foreign Minister Abbas Araqchi on Wednesday admitted that "problems" remained, saying there could not be a deal without a "framework for the removal of all sanctions".

The BBC's Barbara Plett Usher in Lausanne says Mr Araqchi suggested there might be a joint press statement that talks about progress made and continuing to try to draft a solution.

This sounds less than the framework on political parameters which the negotiators had been targeting, our correspondent says.

Chinese Foreign Minister Wang Yi, who has now left Lausanne, issued a note of caution.

A Chinese statement read: "It is important to give political guidance to the negotiations... it is important to narrow down the differences.

BBC