The deadline for an Iran nuclear deal has been extended to the end of June after talks in Vienna failed to reach a comprehensive agreement.

UK Foreign Secretary Philip Hammond said good progress had been made, but it was "not possible to get an agreement by the [original] deadline".

Six world powers want Iran to curb its nuclear programme in return for the lifting of sanctions.

Tehran says it is not seeking nuclear weapons, but wants atomic energy.

The six countries - the US, UK, Russia, China, France and Germany - have been in negotiations with Iran to finalise a preliminary deal reached last year in Geneva.

Speaking after the Vienna talks had ended, Mr Hammond said that negotiations would resume in December, and would be extended until 30 June 2015.

Iran would be allowed to continue accessing $700m (£450m) per month in frozen assets during that period.

Diplomats expect to reach a political agreement by 1 March, with the full technical details of the agreement confirmed by 1 July.
'Maintaining momentum'

Speaking to the BBC, Mr Hammond said that the failure to agree a deal was "a disappointment, but rather than continue blindly we have to recognise the reality that we're not going to make a deal tonight".

He said he was aware that hardliners opposed to any deal were vocal both in Iran and the US, which was why talks would continue again in December.

"We are all clear that enough progress has been made that maintaining the current momentum, and keeping working at it, does give us the prospect of getting to a deal," he added.

Iranian President Hassan Rouhani is to give a national address at 18:00 GMT, Iranian news agencies reported.

There are thought to have been three key sticking points in the negotiations:

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

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.

However, the International Atomic Energy Agency (IAEA) says it has been unable to confirm Tehran's assertions that its nuclear activities are exclusively for peaceful purposes.

The United Nations Security Council has adopted six resolutions since 2006 requiring Iran to stop enriching uranium, with sanctions to persuade Iran to comply.

The US and EU have imposed additional sanctions on Iranian oil exports and banks since 2012, hitting Iran's oil revenue badly.

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. Saudi Foreign Minister Prince Saud al-Faisal visited Vienna at the weekend for talks with US Secretary of State Mr Kerry, though his country is not formally involved in the discussions.

Israeli Prime Minister Benjamin Netanyahu, whose country has not ruled out bombing Iran's nuclear facilities, told the BBC that "no deal is better than a bad deal".

BBC