The vast majority of Americans support diplomacy with Iran to constrain its nuclear program, a survey found Wednesday, amid a stalemate in negotiations to restore a 2015 deal.

A wide-ranging annual survey by the Eurasia Group Foundation found that nearly 79 percent of US voters believe the United States "should continue to pursue negotiations to prevent Iran from obtaining or developing a nuclear weapon in the near future."

Former Republican president Donald Trump pulled out of the accord in 2018, calling it the "worst deal ever," and reimposed sweeping sanctions.

But the survey found that close to 72 percent of Republicans backed nuclear diplomacy with Iran. It did not ask about specific details of the 2015 accord.

President Joe Biden supports a restoration of the accord, but negotiations have repeatedly broken down, with Iran most recently demanding an end to the UN watchdog's probe of previous suspicious activities.

Political pressure has also built on Biden not to give Iran economic relief amid major protests against the clerical state triggered by the death of a young woman in the custody of morality police.

The Eurasia Group Foundation polled 2,002 US adults of voting age from September 2-8.

The survey also found a rise in the percentage of Americans who would back the use of force to expel Russian forces if they invade a NATO ally in the Baltics.

Nearly 65 percent agreed, up from less than 50 percent in 2021, although support was also high in previous years.

Biden has led a campaign to punish Russia and arm Ukraine over Moscow's invasion but has ruled out direct attacks on Russia, a rival nuclear power.

But Biden has warned of a response to any attack on NATO members, in line with the Western alliance's promises of common defence.