"We are committed to diplomacy, but this process cannot go on indefinitely. At some point the gains achieved by the JCPOA (Joint Comprehensive Plan of Action) cannot be fully recovered by a return to the JCPOA if Iran continues the activities that it's undertaken with regard to its nuclear program," he said, addressing a news conference in Kuwait.

"We have clearly demonstrated our good faith and desire to return to mutual compliance with the nuclear agreement ... The ball remains in Iran's court and we will see if they're prepared to make the decisions necessary to come back into compliance."

Indirect talks between Tehran and Washington to revive the nuclear pact, from which then-president Donald Trump withdrew the United States, adjourned on June 20, two days after the hardline cleric Ebrahim Raisi was elected president of the Islamic Republic. Raisi takes office on August 5.

Parties involved in the negotiations have yet to say when they might resume.

Gulf Arab states have asked to be included in the negotiations, and for any deal to address what they call Iran's destabilising behaviour in the region.

The parties to the JPCOA are Iran, the United States, China, Russia, France, Britain, Germany and the European Union.

Blinken arrived in Kuwait on Wednesday and met the emir, Sheikh Nawaf, state media reported.

Australian Associated Press