Tehran officially suspended its cooperation with the IAEA, a move triggered by the unprecedented Israeli and US strikes on its nuclear facilities over 12 days in June.

"We'll use the word unacceptable, that Iran chose to suspend cooperation with the IAEA at a time when it has a window of opportunity to reverse course and choose a path of peace and prosperity," Bruce told a briefing in Washington.

Washington backed Israel's effort to damage Iran's nuclear program by bombing three nuclear sites overnight on June 21-22. Trump has since warned he will order more air strikes if Tehran tries to obtain nuclear weapons.

The Islamic republic has always denied it was seeking to develop an atomic weapon.

Bruce said Iran must cooperate without delay with the IAEA, including by providing "information required to clarify and resolve long-standing questions regarding undeclared nuclear material in Iran, as well as provide unrestricted access to its newly announced enrichment facility."

"Iran cannot and will not have a nuclear weapon," she repeated.