The law, passed by the conservative dominated legislature despite opposition from a reformist government, mandates Iran to discontinue certain inspections by late February if key conditions are not met, stoking international concerns about a possible expulsion of inspectors.

However, foreign ministry spokesman Saeed Khatibzadeh said on Monday that under the December law "Iran's cooperation with the (International Atomic Energy Agency) will not cease and it does not mean expelling the agency's inspectors."

The December law mandated the government to stop "the implementation of the additional protocol" to the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) on February 21, if the US does not lift unilateral sanctions or other key parties to a 2015 nuclear deal with Iran do not help Tehran to bypass those sanctions.

The "additional protocol" is a document prescribing intrusive inspections of Iran's nuclear facilities.

At present, such inspections are carried out under this protocol, in addition to regular IAEA inspections under the 2015 deal, but the additional protocol has never been ratified by Iran's parliament.

Iran's President Hassan Rouhani, a moderate, slammed the December legislation -- known as the "strategic action plan for the lifting of sanctions and the protection of the Iranian people's interests" -- as "detrimental to the course of diplomatic activities" when it was still before parliament.

Former US President Donald Trump unilaterally withdrew Washington from the 2015 multilateral nuclear accord and reimposed sanctions on Tehran in 2018.

Iran in response has retreated from most of its key nuclear commitments under the 2015 deal, which gives the Islamic republic relief from international sanctions in exchange for limits on its nuclear programme.

Rouhani's government has signalled a readiness to engage with US President Joe Biden, who took office on January 20 and who has likewise expressed willingness to return to diplomacy with Tehran.