"Right now I don't see a near-term prospect for that moving forward," Blinken said of the 2015 deal formally known as the Joint Comprehensive Plan of Action.

"Why? Because the Iranians will continue to try to inject extraneous issues into discussions over the JCPOA that are a dead end," Blinken told an event at Bloomberg News.

He vowed that the United States would prevent Iran from developing a nuclear weapon, and added: "We continue to believe that diplomacy is actually the best and most effective way."

His remarks come a day after Iranian President Ebrahim Raisi accused the United States of "dragging their feet" on reviving the agreement, which was rejected by former US president Donald Trump.

President Joe Biden took office hoping to restore the agreement, but his aides have rejected Iranian demands including that the UN nuclear watchdog close its probe of previous suspected nuclear activity.

Any US decision to restore the nuclear accord became even more politically fraught after the outbreak in September of major protests set off by the death of a 22-year-old woman, Mahsa Amiri, who was detained by the notorious "morality police."

"I think what we're seeing across Iran is a quite remarkable expression of frustration, anger at various policies pursued by the regime. And we're seeing this spontaneously," Blinken said.

"We're seeing it in different parts of the country -- what appears to be really from the grassroots."

The Biden administration earlier Wednesday imposed new targeted sanctions on human rights grounds on Iranian officials over the crackdown on the protests.