Iran said it hoped a visit by the head of the UN's atomic watchdog that started on Monday would be "constructive", a week before the resumption of talks to revive the 2015 nuclear deal.
Rafael Grossi, chief of the International Atomic Energy Agency, was greeted on arrival by the spokesman of the Atomic Energy Organisation of Iran, Behrouz Kamalvandi, state news agency Irna reported.
Mr Grossi is expected on Tuesday to meet Foreign Minister Hossein Amirabdollahian and Iranian nuclear leader Mohammad Eslami, who is also one of Iran's vice presidents.
"We hope that Rafael Grossi's visit will be as constructive as the previous ones," Foreign Ministry spokesman Saeed Khatibzadeh said.
"We have always advised the IAEA to stay on the path of technical co-operation and to not let certain countries pursue their political orientations on behalf of the IAEA."
On Friday, the agency said Tehran had again increased its stockpile of highly enriched uranium, many times in excess of the limit in the 2015 agreement.
Iran is preparing for talks with world powers in Vienna on November 29 with the aim of saving the 2015 deal, which brought sanctions relief in return for curbs on its nuclear programme.
On November 12, Mr Grossi had described as "astonishing" his lack of contact with the new Iranian government of President Ebrahim Raisi.
Days later, Tehran responded by announcing that it had invited the watchdog chief to visit.
"We will leave for Vienna with a full team and a serious will to lift the sanctions," Mr Khatibzadeh said on Monday.
"The other parties should also try to come to Vienna to reach a practical and comprehensive agreement."
The deal was all but ended in 2018 when former president Donald Trump withdrew the US from it and imposed punishing sanctions.
Iran has since moved away from many of its commitments, but the administration of US President Joe Biden has advocated a return to diplomacy to save the agreement.
The other parties to the deal – Britain, China, France, Germany and Russia – will join the talks while the US will take part indirectly.
Mr Grossi was last in Tehran on September 12, when he clinched a deal on access to monitoring equipment at Iran's nuclear plants.
On Saturday, US Defence Secretary Lloyd Austin warned that Washington was capable of "overwhelming force", and that all options would be open if diplomacy failed to halt Iran's nuclear programme, which Tehran insists is for peaceful purposes.
Mr Khatibzadeh was sceptical about US military response to failed talks.
"We have seen all their options in a country like Afghanistan and they have seen the outcome of those options. Do not believe what they say," he said.
Robert Malley, the US envoy for Iran, also warned on Friday that Tehran was approaching the point of no return and that "time is short" for reviving a nuclear deal.
But Mr Khatibzadeh accused the US of trying to "sell a false narrative to the international community to create a psychological atmosphere in the run-up to the Vienna talks".
He said it "will not help them at all".