Iran's Rouhani heads to Europe to rescue nuclear deal

President Hassan Rouhani departed Iran on Monday for a trip to Europe billed as of "prime importance" after the US pulled out of the 2015 nuclear deal between Tehran and world powers.

Rouhani was set to visit Switzerland and Austria as part of Tehran's ongoing efforts to secure Europe's continued support for the landmark agreement.

The Iranian president left Tehran on an early afternoon flight and was due to land in Zurich in the mid-afternoon, Iranian state media reported.

His delegation will travel on to Vienna on Wednesday, according to authorities in Austria, where the historic nuclear deal was signed in July 2015. 

The trip will be an "opportunity to talk about the future of the (nuclear) agreement," Rouhani told reporters at Tehran's Mehrabad Airport before boarding his flight, state television showed.

Foreign Minister Mohammad Javad Zarif is also scheduled to hold talks with Swiss officials in Bern.

The visit comes nearly two months after US President Donald Trump unilaterally pulled out of the agreement, to the ire of the other signatories - China, France, Germany, Britain and Russia - which along with the European Union have continued to back the accord. 

Rouhani's European trip will be of "prime importance" as it could "provide a more precise picture of cooperation between Iran and Europe," Iranian foreign ministry spokesman Bahram Ghassemi said in comments carried by the semi-official ISNA news agency on Saturday.

On Sunday, Austria took over the European Union's six-month rotating presidency, while Switzerland represents US interests in Iran owing to the absence of diplomatic relations between Washington and Tehran.

Vienna, where the deal was signed, is also the home of the United Nations' nuclear watchdog, the IAEA, which monitors Iran's compliance with the accord.

The nuclear deal has been the cornerstone of Rouhani's policy of greater openness with the West, and the US departure has seen him severely criticised by ultra-conservatives at home. 

Even before Trump's decision, Iranians had long complained that the hoped-for uptick in foreign investment after the deal had not materialised.

Washington's decision paves the way for new US sanctions against Tehran, which will encompass businesses from third countries that continue to operate in Iran. 

A number of foreign firms have already announced they would cease their Iranian activities in light of the looming imposition of sanctions. 

Failure 'very dangerous'

While in Switzerland, officials are due to sign agreements on economic cooperation, according to Iran's official IRNA news agency.

Rouhani will meet with the Swiss president, Alain Berset, and his two-day visit will coincide with a bilateral economic forum on health and nutrition, although it was not clear whether he will attend in person.

There will be a similar focus on finances in Vienna, where the Iranian president is expected to sign memorandums on economic cooperation according to Austrian media. 

Chancellor Sebastian Kurz said he will speak plainly with Rouhani about Iran's role in the Middle East, as Tehran continues to deny accusations it is destabilising the region.

Kurz will also find "clear words" to discuss the human rights situation in Iran, the chancellor told Austrian news agency APA.

The European tour is part of a broader diplomatic effort by Tehran to rally support in the wake of Trump's May 8 withdrawal from the deal, formally known as the Joint Comprehensive Plan of Action (JCPOA).

Iran's supreme leader, Ali Khamenei, has demanded Europe provide a number of economic guarantees in order for Tehran to continue its commitment. 

Increasing the pressure on Iran's European partners, he ordered preparations be made to quickly restart nuclear activities in case talks collapse.