Iran nuclear deal: Clock ticks on deadline
Time is running out for world powers to strike a deal with Iran to cut UN sanctions in return for action to scale back its nuclear programme.
With major differences remaining, it appears likely the talks will be extended until the summer of next year, diplomatic sources in Vienna say.
Iran and the six powers it is negotiating with had set themselves a deadline of 23:00 GMT to reach a deal.
Tehran says it is not seeking nuclear weapons, but wants atomic energy.
The US, UK, Russia, China and France, plus Germany, are trying with Iran to finalise a preliminary deal reached last year in Geneva.
High-level meetings continued on Monday morning between Iranian Foreign Minister Javad Zarif, US Secretary of State John Kerry and the other five nations' foreign ministers.
Over the past few months the talks have reduced fears of a new Middle Eastern war and the ministers will be reluctant to leave Vienna without a way forward, the BBC's Bethany Bell reports from Vienna.
Diplomatic sources said the talks would be extended until 1 July.
At the scene: Mohsen Asgari, BBC News, Tehran
The nuclear crisis has become part of everyday life in Tehran but with still no outcome in Vienna, ordinary people are not talking about it that much. Iranians have been listening to the same repetitive news story for the past seven days and they simply do not want to discuss it until something actually happens.
"I am fed up with these boring stories saying the same thing 24 hours a day - either do something or give up," said a middle-aged man sitting in a taxi as soon as the morning news bulletin began on the radio.
Last night's football derby in Tehran was a good opportunity for people and journalists to talk about something else. In fact, the death of a young pop star from cancer last week is still being discussed more than what may or may not be happening in the Austrian capital.
The proposed agreement hinges on the rate at which the sanctions against Iran would be lifted if Tehran agreed to highly specific limits on the amount of uranium it could enrich.
Highly enriched uranium can be used to make a nuclear bomb, but uranium enriched to lower levels can be used for energy purposes.
Under the terms of international treaties, countries have the right to develop nuclear energy, which Iran insists is its only aim.
Analysis: Jeremy Bowen, BBC Middle East editor, Vienna
Success would do much to lift Iran's isolation - which would change the strategic balance in the Middle East. That intrigues some Western diplomats. It horrifies Saudi Arabia and Israel.
A year ago in Geneva all sides in the talks saw an opportunity to deal with an issue that could potentially cause another catastrophic war. That will make them very reluctant to leave Vienna empty-handed - even if that means they will have to do more work on the details next year.
Time is limited though. Hardliners in Tehran and Washington DC will try to sabotage any agreement. Both see no reason to dilute their mutual suspicion.
Under an agreement reached in Geneva last year, Iran was to curb some of its uranium enrichment in return for sanctions relief.
However, the two sides failed to reach a lasting deal by July, as initially agreed, and extended the deadline until 24 November.
Some of the major obstacles to the deal include:
- Western states want to reduce Iran's capacity for uranium enrichment in order to prevent it acquiring weapons-grade material but Tehran is set on expanding it nearly twentyfold in the coming years
- Iran wants sanctions lifted immediately but Western states want to stagger their removal to ensure Tehran abides by its commitments
- Iran has failed to explain explosives tests and other activity that could be linked to a nuclear weapons programme and has denied international nuclear inspectors access to its Parchin military site
US President Barack Obama acknowledged on Sunday that "significant" gaps between the two sides remained, and that President Hassan Rouhani had "to deal with his politics at home".
"He's not the ultimate decider inside of Iran, the Supreme Leader [Ayatollah Ali Khamenei] is," Mr Obama told US broadcaster ABC.
Both Saudi Arabia and Israel are also vehemently opposed to Iran acquiring nuclear weapons and Saudi Foreign Minister Prince Saud al-Faisal visited Vienna at the weekend, though his country is not formally involved in the talks.
He and Mr Kerry talked in his plane parked at Vienna Airport on Sunday, diplomats told AP news agency.
Israeli Prime Minister Benjamin Netanyahu, whose country has not ruled out bombing Iran's nuclear facilities, welcomed reports that the talks were likely to be adjourned.
"No deal is better than a bad deal," he told BBC News. "The deal that Iran was pushing for was terrible. The deal would have left Iran with the ability to enrich uranium for an atom bomb while removing the sanctions."
Iranian press review, by BBC Monitoring
Papers across the political spectrum display a mixture of hope and defiance. The two sides have reached the "point of no return", says the reformist Sharq, and agreement will be reached "if the other side abstains from raising its expectations", thinks Arabic-language Al-Vefagh.
The conservative Khorasan says that, even if the talks fall through, Iran's economy will take only a minor hit, as it will be able to adapt with the help of Russia and China. The reformist Etemaad is certain that world opinion will blame any failure on the West, as Iran has been "serious about reaching an agreement". The moderate paper Iran says failure is "unimaginable", as the consequences would be serious for the US.
But the conservative Resalat says that a deadline extension would mean negotiators can "continue this game for longer", and that, whatever the outcome, it will only lead to "even louder shouts of Death to America and Death to Israel".