VIENNA • Only "a few" remaining hurdles need to be cleared to reach an unprecedented deal with Iran curtailing its nuclear programme, according to an Iranian official.

Foreign ministers chasing a deal by today's deadline met yesterday for their first full session in the latest round of talks.

Three months ago, there were a number of unresolved issues, the official said, asking not to be identified. But now "there are only a few items left which need to be tackled by the ministers. That is why the ministers are here", he said.

Experts who have been meeting in Vienna "have moved a lot further" but "there are tough issues... which were not resolved at expert level or the deputy minister level, those are not easy issues".

Britain, China, France, Germany, Russia and the United States are seeking to end a 13-year stand-off with Iran which began when dissidents revealed its nuclear programme in 2002. Teheran has long denied seeking to develop nuclear arms and, in return for curtailing its atomic industry, is demanding an end to biting economic sanctions.

A dispute over United Nations sanctions on Iran's ballistic missile programme is among the issues holding up the nuclear deal, both Iranian and Western officials said.

"The Iranians want the ballistic missile sanctions lifted. They say there is no reason to connect it with the nuclear issue, a view that is difficult to accept," a Western official said.

A mechanism for quickly re-imposing sanctions if Iran breaks the deal is also a hurdle blocking an accord. Teheran wants a reciprocal so-called "snapback" measure.

"If there are issues that we have, for instance, in regard to sanctions termination, the same procedure has to be applied to those issues as well," the Iranian official said. "To put it broadly, snapback is something that needs to be provided to all sides, not only one side."

He insisted that Iran had already "made a number of concessions, we have shown a good amount of flexibility". This round of talks in Vienna has already busted a June 30 deadline, and is now in its 10th straight day. But all sides have insisted they are not planning a further extension beyond today's new deadline. The Iranian delegation had not even discussed "a possible extension because extension, to be honest, is not in anybody's interest", the official said.

But he conceded: "If we need to stay some more days in Vienna, it is much better to spend some more time here than to go home and then come back."

US Secretary of State John Kerrysaid on Sunday "it is now time" to seal the deal.

"While I completely agree... that we have never been closer, at this point, this negotiation could go either way," he said, with talks "not yet where we need to be on several of the most difficult issues".

The point was rammed home by France's Foreign Minister Laurent Fabius, Germany's Mr Frank-Walter Steinmeier and European Union foreign policy chief Federica Mogherini as they returned to Vienna late on Sunday. "The main question is to know whether the Iranians will accept making clear commitments on what until now has not been clarified," Mr Fabius said.

Also present were Russian Foreign Minister Sergei Lavrov and China's Wang Yi, who said yesterday that a "comprehensive agreement is within reach".

"What is important is that today and tomorrow, all parties, especially the US and Iran, should make their final decisions as quickly as possible," Mr Wang said.

AGENCE FRANCE-PRESSE, REUTERS