Supreme Leader Ayatollah Ali Khamenei has criticised President Hassan Rouhani for saying his policy of detente with the West had reduced the threat of Iran becoming involved in a war.

Sunday's statement came as tensions intensify in Tehran before the presidential election on May 19.

Rouhani - a pragmatist whose election in 2013 led to a diplomatic thaw between Iran and the West - championed a landmark deal in 2015, in which Tehran agreed to curb its nuclear programme in return for the lifting of international sanctions.

A standoff between Rouhani, who is seeking a second term, and Khamenei's allies, who opposed the nuclear deal, has intensified in recent months in the run-up to the vote.

"Some say since we took office the shadow of war has been faded away. This is not correct," Khamenei was quoted as saying by state media on Sunday.

"It's been people's presence in the political scene that has removed the shadow of war from the country," he added.

Criticism on economy

Rouhani faces competition from hardliners who have criticised his economic record, saying rapprochement with the West and nuclear concessions had yet to yield economic benefits.

"The nuclear deal was a national achievement. We should make use of its advantages. But some have started a fight over it," Rouhani said on Sunday.

Opening a refinery in the southern city of Bandar Abbas, Rouhani said the project - which makes Iran self-sufficient in petroleum production - was a result of the nuclear deal and "interaction with the world".

Rouhani urged voters on Saturday to prevent "extremism" from returning to Iran, saying the country could face greater authoritarianism if he was replaced by a hardline rival.

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Among Rouhani's challengers are Ebrahim Raisi, an influential religious leader with decades of experience in the hardline judiciary, and conservative Tehran Mayor Mohammad Baqer Qalibaf, a former Revolutionary Guards commander.

Wary of US President Donald Trump's tough talk on Iran, the European Union is courting Tehran to show Iranians preparing to vote that the EU is committed to the nuclear deal and they stand to benefit, diplomats said on Sunday.

Europe's energy commissioner is leading more than 50 European firms in a business forum in Tehran over the weekend - the latest bid to foster new ties in the 16 months since Iran curbed its nuclear programme in exchange for sanctions relief.

Of the six major powers who engineered the deal - the United States, Britain, France, Germany, China and Russia - EU nations bore the brunt of the oil embargo on Iran and stand to gain the most from a thaw they view as a victory for European diplomacy.

Meeting with Iran's atomic chief Ali Akbar Salehi, Commissioner Miguel Arias-Canete echoed the EU's mantra that it is "fully committed" to the 2015 deal and expects the same from all other parties.

But the bloc's leverage remains limited - particularly if it is not able to shield European firms from the risk of remaining US sanctions and encourage big banks to reverse more than a decade of Iran's exclusion from the international financial system.

FEATURE: Iranians still waiting for dramatic economic change

Some Western companies have returned - aircraft manufacturers Airbus and Boeing and car-makers Peugeot-Citroen and Renault - but many more have hung back, fearing Trump will tighten the screws on an already complex set of rules for engaging with Iran.

The Trump administration said on April 18 that it was launching an inter-agency review of whether the lifting of sanctions against Iran was in the US' national security interests, while acknowledging that Tehran was complying with the deal to rein in its nuclear programme.

"There is a lot of enthusiasm about working with Iran now and ... I hope that the American administration wakes up to these realities," Iran's Vice President Masoumeh Ebtekar told Reuters news agency.