Iran dismissed Thursday a call by the US for it to return to full compliance of a nuclear deal first, insisting it had only taken "remedial measures" since America's withdrawal.
The administration of new US President Joe Biden on Wednesday confirmed its willingness to return to the deal, which has been hanging by a thread since his predecessor Donald Trump's decision to withdraw from it in 2018.
But Secretary of State Antony Blinken, who made the announcement, said the US would only return to the deal agreed with major powers in 2015 once Iran resumes its commitments.
Iran's top diplomat, Mohammad Javad Zarif, on Thursday dismissed the demand.
"Reality check for @SecBlinken: The US violated (the) JCPOA," Zarif tweeted, referring to the accord by its formal name, the Joint Comprehensive Plan of Action.
Zarif said that as well as its unilateral withdrawal, the US had also imposed sanctions that "blocked food/medicine to Iranians" and "punished adherence" to a UN resolution.
"Now, who should take 1st step? Never forget Trump's maximum failure," the foreign minister added, stressing Iran had "abided by the JCPOA" and had only taken "foreseen remedial measures".
Trump withdrew the US from JCPOA and imposed crippling sanctions on Iran in 2018, maintaining a policy of "maximum pressure" against the Islamic republic.
Iran a year later responded by suspending its compliance with most key nuclear commitments in the deal, under which it was promised economic relief for limits on its nuclear programme.
On January 4, Iran announced it had stepped up its uranium enrichment process to 20 percent purity, far above the 3.67 percent level permitted by the deal, but far below the amount required for an atomic bomb.
Tehran has called on Washington to "unconditionally" lift sanctions imposed by Trump to salvage the nuclear deal.
It has said it will return to full compliance once all parties to the accord fullfil their commitments to the agreement.