Iran's supreme leader on Wednesday declared Tehran would not accept Washington's "stubborn" demands in talks to revive a 2015 nuclear deal and said the United States had failed to guarantee that it would never abandon the pact again.

"The Americans acted completely cowardly and maliciously," state TV quoted Ayatollah Ali Khamenei as saying.

Like Khamenei, Raisi has backed the revival of the nuclear pact but officials have said that his government might adopt "a hardline" approach. Khamenei, not the president, has the last say on Iran's state matters, including the nuclear policy.

Iranian and Western officials have said significant gaps remained to reinstate the deal, under which Iran agreed to curb its nuclear program to make it harder to obtain fissile material for a weapon in return for relief from tough sanctions.

U.S. President Joe Biden seeks to reinstate and eventually broaden the pact to put more limits on Iran’s nuclear work and its missile development and constrain its regional activities.