Enrique Mora's visit "is a follow-up to consultations between the two sides on matters of shared interest, particularly Iran-EU relations, Afghanistan and the nuclear agreement," a ministry statement said.

The deal, which gave Iran sanctions relief in return for curbs on its nuclear programme, has been on life support since 2018, when then US president Donald Trump unilaterally pulled out and reimposed crippling sanctions.

Mora's trip to Tehran comes amid mounting pressure from EU countries as well as the United States for a swift resumption of talks on Washington's return to the agreement.

"The message to Iran is unequivocal: return to the negotiating table immediately," German Chancellor Angela Merkel said during a visit to Israel on Sunday.

Tehran has been seeking European guarantees that there will be no repetition of Trump's unilateral withdrawal.

"The European capitals, including Berlin... must give their clear assurance to the Islamic republic that this time, no party will violate the nuclear deal," foreign ministry spokesman Saeed Khatibzadeh told reporters on Monday.

US President Joe Biden has signalled a willingness to return to the deal, but his Secretary of State Antony Blinken warned earlier this month that time was running out and the ball was in Iran's court.

Talks in Vienna between Iran and the remaining parties to the agreement -- Britain, China, France, Germany and Russia -- have been on hold since a June election in Iran led to a change of president.

New President Ebrahim Raisi -- an ultraconservative former judiciary chief -- is thought to be less ready than his predecessor Hassan Rouhani to make concessions to the West for the sake of a deal.

Iran has said repeatedly that it is ready to resume talks "soon" but no date has yet been announced.

Tehran gradually rolled back its own nuclear commitments in response to the US pullout, and Washington has been demanding that it return to its obligations too.

Mora attended Raisi's inauguration in August, drawing criticism of the EU from Israel, a fierce critic of the nuclear deal with its arch foe Iran.