DUBAI (Reuters) - Iran on Sunday ruled out holding an informal meeting with the United States and European powers to discuss ways to salvage the unravelling 2015 nuclear deal with major powers, insisting that Washington must first lift all its unilateral sanctions. “Considering the recent actions and statements by the United States and three European powers, Iran does not consider this the time to hold an informal meeting with these countries, which was proposed by the EU foreign policy chief,” Foreign Ministry spokesman Saeed Khatibzadeh said, according to Iranian media. The United States said it was disappointed, but that it remained ready to “re-engage in meaningful diplomacy” on the issue. Iranian officials had said Tehran was studying a proposal by European Union foreign policy chief Josep Borrell to hold an informal meeting with other parties to the nuclear pact and the United States, which reimposed sanctions on Iran after then-president Donald Trump quit the deal in 2018. The new administration of President Joe Biden has said it is ready to talk to Iran about both nations returning to the accord, which scrapped United Nations sanctions against Iran in return for curbs intended to prevent it acquiring nuclear weapons - something Iran says it does not want. But the parties cannot agree who should make the first move. Iran says the United States must lift sanctions while Washington says Tehran must return to compliance with the deal, which it has been progressively breaching. A White House spokeswoman said Washington remained keen to achieve a “mutual return to compliance” with the deal. She said it would consult with its partners who are signatories - China, France, Russia, Britain and Germany - on the best way forward. NUCLEAR WATCHDOG TO MEET One senior U.S. source said Iran’s rejection was simply part of the diplomatic process. Earlier on Sunday, Iran’s nuclear chief urged the International Atomic Energy Agency’s (IAEA) 35-nation Board of Governors not to endorse a U.S.-led push to criticise Tehran’s decision to scale back its cooperation with the U.N. nuclear watchdog. “If the IAEA’s Board of Governors adopts a resolution against Iran, we will show an appropriate reaction,” Ali Akbar Salehi said, according to the Iranian state news agency IRNA. In a position paper seen by Reuters that was sent to other IAEA member states ahead of the board’s quarterly meeting this week, Tehran threatens to end a deal struck with the IAEA a week ago temporarily maintaining some monitoring of its activities. Diplomats said it was still unclear whether the board would adopt a resolution. On Feb. 23, Tehran stopped implementing the so-called Additional Protocol, which had enabled the IAEA to carry out snap inspections at undeclared locations. But under the Feb. 21 agreement, Tehran agreed to maintain the recording of extra data as specified by the 2015 deal for up to three months, and to let the IAEA access it at the end if sanctions were lifted. Khatibzadeh said that, for the United States to “end its illegal and unilateral sanctions and return to its commitments”, there was no need for “negotiation or a resolution in the U.N. nuclear watchdog’s Board of Governors”.