The five United Nation veto powers and Germany failed to agree on an initial nuclear deal with Iran that would have asked for mutual concessions, after three days of high-level talks in Geneva.

“A lot of concrete progress has been made, but some differences remain,” said Catherine Ashton, chief negotiator for the group of Britain, China, France, Russia, the United States and Germany.

The issue of stopping construction of a plutonium-producing plant was one of the key sticking points, according to French Foreign Minister Laurent Fabius.

A new round of talks to clinch a temporary deal on halting parts of Iran’s nuclear programme in return for suspension of some sanctions was scheduled for November 20-21 in Geneva.

“Our goal continues to be a comprehensive solution to prevent a nuclear-armed Iran,” German Foreign Minister Guido Westerwelle said.

The planned agreement fell through after intensive negotiations led by foreign ministers and other senior officials from all involved countries.

The talks included lengthy meetings between two leaders whose countries officially have no diplomatic relations: Iranian Foreign Minister Mohammad Javad Zarif and US Secretary of State John Kerry.

Kerry said talks were taking time because longstanding distrust between Iran and the West needed to be overcome.

But he also warned that the talks could not last forever. “The clock is ticking,” he said.

Since Iran’s covert nuclear programme came to light 10 years ago, the six powers, known as the P5+1 or E3+3, have been trying to negotiate a halt of Tehran’s atomic activities, out of fear that they are part of a nuclear weapons programme.

Iran has been stressing that it only needs the technology to make electricity and for other civilian uses.

In the deal discussed this week in Geneva, the group aimed to halt Iran’s current efforts to enrich uranium to 20 per cent.

The six countries are concerned that such material can easily be used in a nuclear warhead, while Iranian leaders insist the uranium will only fuel a research reactor.

Fabius told France Inter radio that the French delegation insisted Tehran halt construction of a new reactor at Arak, which would produce plutonium that could be used in nuclear warheads.

Various media reports suggested that France’s hardline stance prevented an agreement.

But Kerry backed Fabius on the Arak issue and told reporters that it must be addressed as part of any sort of agreement.

Iran’s Zarif avoided criticising the French. “I think we expect all different members of the E3+3 to have their views,” he said.

Zarif said he was “not disappointed at all” by the lack of an agreement and was hoping for a deal at the next round of talks.

Iran has been demanding that embargoes be lifted on oil exports and the banking sector, and it would especially like to see those sanctions suspended that most directly affect the general public.

Western officials had described the prospective deal as a first set of confidence-building steps to be implemented for a limited time to pave the way to a more comprehensive agreement.

The diplomatic drive has opened a rift between the US and Israel, which is convinced that Iran is seeking atomic weapons that endanger Israel’s existence.

Israeli Prime Minister Benjamin Netanyahu lashed out Friday at the group of six for planning a deal that would not completely stop Iran’s atomic programme. He made clear that his country would stick to its option of attacking Iranian nuclear sites, should diplomatic efforts fail.

Kerry said the US would keep protecting Israel, but he also stressed that all efforts must be made to deal with Iran through talks.