UN nuclear watchdog head Rafael Grossi was to open talks Saturday in Iran on the eve of Tehran's deadline for US sanctions to be lifted, as President Joe Biden called for "careful diplomacy".
The deadline, set by Iranian lawmakers, carries the threat of a suspension of some nuclear inspections, stoking international concern about a possible expulsion of UN inspectors.
But Iran has stressed it will not cease working with the International Atomic Energy Agency (IAEA) or expel its inspectors.
Iran and the IAEA have yet to release details on the visit by the UN body's chief Grossi that runs into Sunday.
He will "meet with senior Iranian officials to find a mutually agreeable solution, compatible with Iranian law, so that the @iaeaorg can continue essential verification activities in Iran", Grossi wrote Friday on Twitter.
"Looking forward to success – this is in everybody’s interest," he added.
Iran has notified the IAEA that it will suspend "voluntary transparency measures", notably inspection visits to non-nuclear sites, including military sites suspected of nuclear-related activity, if the United States has not lifted the sweeping sanctions former president Donald Trump reimposed in 2018.
The new measures are to go into effect on Tuesday.
Iran's atomic body spokesman Behrouz Kamalvandi said last week that talks with Grossi will focus on how to cease "voluntary actions beyond safeguard (measures) and how to continue cooperation".
- 'Diplomatic back-and-forth' -
The visit comes in the wake of Biden's call on Friday for European powers to work together to curb Iran's "destabilising" activities, a day after committing to rejoin talks on Tehran's nuclear programme.
Biden told the Munich Security Conference that the United States would work closely with allies in dealing with Iran after his predecessor Trump took an aggressive unilateral approach.
"The threat of nuclear proliferation also continues to require careful diplomacy and cooperation among us," Biden told fellow leaders via teleconference.
"That's why we have said we're prepared to reengage in negotiations with the P5+1 on Iran's nuclear program," he said, referring to the five UN Security Council permanent members and Germany.
Tehran has repeatedly said it is ready to return to its nuclear commitments on condition that Washington does so first by lifting the sanctions reimposed by Trump that have dealt a heavy blow to Iran's economy.
Following an offer for talks by the Biden administration, Foreign Minister Mohammad Javad Zarif tweeted Friday that Iran would "immediately reverse" its retaliatory measures if the US lifts "all sanctions imposed, re-imposed or re-labelled by Trump".
The former president withdrew from the nuclear accord in 2018, while Iran started the next year to suspend its compliance with most key nuclear commitments in response.
In an opening gesture, the Biden administration has dropped a push for more sanctions crafted by Trump, and removed restrictions on Iranian diplomats accredited to the United Nations in New York.
Iran's government spokesman Ali Rabiei on Saturday stressed that Tehran's latest nuclear move will not prevent it from responding to any US show of goodwill, and expressed optimism regarding the ongoing diplomatic process.
It is "neither against our (deal) commitments nor an obstacle for proportionate and appropriate response to any US action to prove (its) goodwill," he wrote in an op-ed on Iran daily.
"We can confidently predict that diplomatic initiatives will work well (to achieve) the desired outcome, despite diplomatic back-and-forths, which are the natural prelude to the return of all sides to commitments including the lifting of all sanctions in the near future," he added.