An Iranian flag is pictured at the United Nations headquarters in New York, Jan. 8, 2020. (Xinhua/Li Muzi)

UN nuclear watchdog head Rafael Grossi arrived late Saturday in Iran for talks on the eve of Tehran's deadline for US sanctions to be lifted, as US 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.

Grossi was received in Tehran by Iran's ambassador to the IAEA, Kazem Gharibabadi, and Iran Atomic Energy Organisation official Behrouz Kamalvandi, Gharibabadi tweeted Saturday evening. The IAEA chief's visit was due to run into Sunday.

On Friday, Grossi tweeted he would "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."

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 US has not lifted the sweeping sanctions former president Donald Trump reimposed in 2018.

The new measures, laid out in a law passed by the conservative-dominated parliament in December, are to go into effect on Tuesday, the head of Iran's atomic body, Ali Akbar Salehi, confirmed on Saturday.

AFP