Iran has renewed its call for the United States to lift all sanctions imposed by former president Donald Trump, after an offer for talks from new President Joe Biden's administration.

Foreign Minister Mohammad Javad Zarif tweeted that Iran would "immediately reverse" its retaliatory measures if the US "unconditionally & effectively" lifts "all sanctions imposed, re-imposed or re-labelled by Trump".

The Biden administration has 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 a nuclear deal on the brink of collapse.

Ahead of a Sunday deadline set by Iran for it to restrict some access to nuclear inspectors from the United Nations unless Mr Trump's sanctions are ended, new US Secretary of State Antony Blinken warned jointly with European powers that the move would be "dangerous".

Hours after Mr Blinken's video conference with his French, British and German counterparts, European Union political director, Enrique Mora, proposed via Twitter an "informal meeting" involving Iran - and the US accepted.

"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 - the UK, China, France, Russia, the US and Germany - sealed the 2015 deal brokered by then president Barack Obama under which Iran drastically scaled back its nuclear programme in exchange for promises of economic relief.

Mr Trump withdrew from the deal in 2018 and reimposed sweeping sanctions, aiming to bring Iran to its knees.

Mr Zarif's tweet did not explicitly address the Biden administration's offer of talks.

Iran has demanded an end to Mr Trump's sanctions before reversing protest measures it took away from full compliance.

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 on condition of anonymity.

The UK welcomed the proposed talks and said it would participate.

Mr Biden has insisted he will not remove Mr Trump's sanctions until Iran returns to compliance, but the administration yesterday reversed two symbolic steps by the last administration.

In a letter to the UN, the US said it no longer believed that the world body had "snapped back" sanctions on Iran.

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Mr Blinken's predecessor Mike Pompeo last year argued the United States was still a "participant" in the Security Council resolution that approved the nuclear deal - despite withdrawing later - and therefore could reimpose sanctions.

The argument had been dismissed by the United Nations and close US allies at the time.

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," Iran's top diplomat wrote.

The Biden administration also reversed draconian 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 (IAEA) if the US does not lift its sanctions imposed since 2018 by Sunday.

IAEA chief Rafael Grossi is to travel to Tehran tomorrow for talks with the Iranian authorities to find a solution.

A joint statement by the four foreign ministers after the virtual 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 adamantly opposed by Iran's regional rivals Israel and Saudi Arabia, which both enjoyed tight 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 - a key advocate of nuclear diplomacy with global powers - is set to step down after serving the maximum two consecutive terms, and a more hardline figure is likely to replace him.