Iran on Friday renewed its call for the United States to lift all sanctions imposed by former president Donald Trump, a day after the Biden administration offered to hold talks on reviving the 2015 nuclear deal from which his predecessor withdrew in 2018.
Iran will "immediately reverse" its retaliatory measures if the US "unconditionally and effectively" lifts "all sanctions imposed, reimposed or relabelled by Trump", Iranian Foreign Minister Javad Zarif said on Twitter.
The Biden administration on Thursday offered talks with Iran led by European allies and reversed two largely symbolic steps against Tehran imposed by Mr Trump, as it sought to salvage the nuclear deal aimed at preventing Tehran from developing atomic weapons.
Iran said it would restrict access provided to UN nuclear inspectors from Sunday unless Mr Trump's sanctions are lifted, a further breach of the terms of the 2015 pact.
US Secretary of State Antony Blinken warned jointly with European powers that the move would be dangerous, after speaking to his French, British and German counterparts on Thursday.
Hours later, the US accepted a proposal by European Union political director Enrique Mora for an "informal meeting" involving Iran.
"The United States would accept an invitation from the European Union High Representative to attend a meeting of the P5+1 and Iran to discuss a diplomatic way forward on Iran's nuclear programme," said State Department spokesman Ned Price.
The P5+1 – comprising UN Security Council permanent members Britain, China, France, Russia and the US, plus Germany – sealed the 2015 deal brokered by US president Barack Obama under which Iran drastically scaled back its nuclear programme in exchange for promises of economic relief.
Mr Trump reimposed sweeping sanctions on Iran after pulling the US out of the pact three years later, citing Iran's missile development programme and regional interference.
Mr Zarif's tweet did not explicitly address the Biden administration's offer of talks.
Iran has demanded an end to US sanctions before reversing its breaches of the pact since 2018.
A senior US official said the Biden administration was showing good faith and saw a meeting as the start of a "prolonged path" to restoring and building on the nuclear accord.
If Iran declines to meet, "I think it would be both unfortunate and at odds with their stated view that they want to come back if you come back".
"That's not going to happen simply by one side telling the other one what to do," the official said.
Britain welcomed the proposed talks. "The UK will participate," a spokesperson said.
However, Britain's junior foreign minister told the BBC on Friday that the West should not send signals that it is prepared to overlook Tehran's breaches of the accord.
"I don't think that we should be sending a signal that we are going to overlook this non-compliance or just brush it under the carpet," said James Cleverly, who covers the Middle East and North Africa.
"This is in Iran's hands, they are the ones breaching the conditions of the [deal], they are the ones that can do something about this, and they should come back into compliance," he said.
Joe Biden said he will not remove Mr Trump's sanctions until Iran returns to compliance – but the administration on Thursday undid two symbolic steps by the previous administration.
In a letter to the United Nations, the US said it no longer believed that the world body had "snapped back" sanctions on Iran.
Mr Blinken's predecessor, Mike Pompeo, last year said that the US was still a participant in the Security Council resolution that blessed the nuclear deal, despite withdrawing later, and therefore could reimpose sanctions.
The argument was dismissed by the UN and close US allies.
In his tweet, Mr Zarif said Iran agreed with the Biden administration's decision.
"US acknowledged Pompeo's claims" regarding UN Security Council Resolution 2231 "had no legal validity. We agree," he wrote.
The Biden administration also reversed curbs on Iranian diplomats in New York who were barred from all but a few blocks around the UN and their mission.
Under the terms of a bill adopted by its conservative-dominated parliament in December, Iran will restrict some inspections by the International Atomic Energy Agency if the United States does not by Sunday lift its sanctions imposed since 2018.
IAEA chief Rafael Grossi will to travel to Tehran on Saturday for talks with the Iranian authorities to find a solution.
A joint statement by the four foreign ministers after the online meeting convened by France urged "Iran to consider the consequences of such grave action, particularly at this time of renewed diplomatic opportunity".
The US and Iran have had no diplomatic relations for four decades but they began frequent contact to negotiate the 2015 nuclear deal.
The nuclear accord was opposed by Iran's regional rivals Israel and Saudi Arabia, which both enjoyed close partnerships with Mr Trump.
While Iran's policy is ultimately determined by supreme leader Ayatollah Ali Khamenei, Iranian presidential elections in June add another time pressure factor.
President Hassan Rouhani, an advocate of nuclear diplomacy with global powers, will step down after serving the maximum two consecutive terms, and a more hardline figure is likely to replace him.