The European Union's political director earlier this month proposed the informal meeting involving Iran and the United States. US President Joe Biden's administration has accepted in principle.

Following Biden's election, Washington, the European parties to the deal -- France, Germany and Britain -- and Tehran have been trying to salvage the 2015 nuclear accord, which granted Iran international sanctions relief in return for restrictions on its nuclear programme.

The accord has been nearing collapse since former president Donald Trump unilaterally withdrew in 2018 and reimposed crippling sanctions as part of a "maximum pressure" campaign against Tehran.

"Considering the recent positions and actions of the United States and the three European countries, (Iran) does not consider the time suitable to hold the informal meeting proposed by the European coordinator", foreign ministry spokesman Saeed Khatibzadeh said in a statement.

"There has still been no change in the US positions and behaviour yet," he added, saying the Biden administration has continued "Trump's failed policy of maximum pressure".

Biden has signalled readiness to revive the deal, but insists Iran first return to all its nuclear commitments, most of which it suspended in response to the sanctions, while Tehran demands Washington take the first step by scrapping the sanctions.

The US "has not even announced its commitment to fulfilling its responsibilities" under the deal and the United Nations Security Council resolution that enshrined it, Khatibzadeh said.

He added: "America must end its illegal and unilateral sanctions and return to its (deal) commitments. This needs neither negotiations nor resolutions."

Iran "will answer action with action, and just as it will return to (deal) commitments in accordance with the lifting of sanctions, it will respond to hostile actions and behaviours in the same way".

Iran last Tuesday started to restrict some site inspections by the UN nuclear watchdog, in continuation of suspended nuclear commitments in response to the US failure to lift its sanctions.

Khatibzadeh said Tehran would continue to consult with other parties to the nuclear agreement, and European Union Foreign Minister Josep Borrell "in his capacity as the (deal) coordinator, both bilaterally and multilaterally".