Iran nuclear talks Vienna
Iranian Foreign Minister Javad Zarif talks to journalists as he stands on the balcony of Palais Coburg, the venue for nuclear talks, Austria Leonhard Foeger/Reuters

The decade-long standoff between the Western world and Iran is expected to come to an end as a landmark comprehensive agreement on Tehran's nuclear activities is expected to be announced in Vienna later in the day.

The permanent nuclear deal, which remained elusive for 12 years, will come after 18 days of intense uninterrupted talks between Iran and and the P+1 powers – the US, Britain, China, Russia, France and Germany.

Foreign ministers of all the seven countries and the EU's Foreign Policy Chief Federica Mogherini are to release a joint statement along with a photo opportunity in a press conference later in the day.

A Western diplomatic source told Russian news agency Sputnik International: "Approval of the document will take place at 10:30 am [local time, 08:30 GMT] at Vienna International Centre."

According to the final draft, UN inspectors will also have access to Iranian nuclear sites, which are suspected to be used for covert military activities, Reuters reports, citing a diplomatic source. All the delegates involved in the negotiations spoke on strict condition of anonymity due to sensitivity surrounding the matter.

The final text of the agreement runs up to 100 pages though it is unclear how much of the content will be released during the press conference. Diplomats have hinted that there will be no immediate lifting of the economic sanctions on Iran and it would only be gradual.

All the parties involved in the discussions were cautious in their public remarks. The official English Twitter account of Iranian President Hassan Rohani deleted a post and later posted an amended comment.

When quizzed about the developments, White House spokesperson Josh Earnest told reporters: "They're not going to sign an agreement until all of our concerns have been addressed. And as long as they continue to make progress in doing that, then the talks will, will continue."

Pressure has also been mounting on the ministers and diplomats to seal the deal. With increasing fatigue creeping in, the delegates are expected to leave the Austrian capital to deal with other commitments.