"There is no agreement in the offing, even as we continue to be willing to explore diplomatic paths," Blinken said at the Council on Foreign Relations in New York.

"We'll see by their actions," Blinken said of the future relationship, calling on Iran to choose to "not take actions that further escalate the tensions" with the United States and in the Middle East.

President Joe Biden took office with hopes of returning to a 2015 nuclear accord with Iran scrapped by his predecessor Donald Trump. But EU-mediated talks collapsed and mass protests in Iran made Washington increasingly hesitant to strike a deal with the clerical state.

But diplomats say that indirect talks have quietly resumed in recent months with Oman as an intermediary, with the focus largely on the status of US prisoners in Iran.

The talks on restoring the 2015 nuclear accord broke down over disputes on the extent of relief from sweeping US sanctions imposed by Trump and over when Iran would return to compliance by pulling back from countermeasures taken in response to the US withdrawal from the deal.

Blinken said that the Biden administration had made a "good-faith effort" with European powers as well as rivals China and Russia to return and that for a time "that looked possible."

"Iran either couldn't or wouldn't do what was necessary to get back into compliance," he said.