The talks come a day after US Secretary of State Antony Blinken warned of "other options" if diplomacy fails, as his visiting Israeli counterpart reserved the right to use force.

The 2015 nuclear deal, which gave Iran sanctions relief in return for curbs on its nuclear activities, has been on life support since 2018, when then US president Donald Trump unilaterally pulled out.

Trump reimposed crippling sanctions while Iran, which insists its nuclear programme is for civilian purposes only, gradually rolled back its own commitments.

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.

Iran's foreign ministry said 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".

Bagheri, in charge of the nuclear file for Iran, tweeted that the meeting would include talks about the "removal of cruel sanctions".

- 'Other options' -

US President Joe Biden, who took office in January, has signalled a willingness to return to the nuclear deal.

Talks were held earlier this year in Vienna between Iran and the remaining parties to the agreement -- Britain, China, France, Germany and Russia -- with the US taking part indirectly.

The talks 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.

Blinken told reporters on Wednesday that he hoped for the success of talks with Iran but warned that "the runway that we have left to do that is getting shorter and shorter".

Referencing visiting Israeli Foreign Minister Yair Lapid's threat to use force, Blinken said without elaborating: "We are prepared to turn to other options if Iran doesn't change course."

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

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.