Tensions between Iran and the West have spiked in recent months, following Tehran's brutal suppression of protestors and drone shipments to Russia.
The Iran nuclear deal "is dead", US President Joe Biden has said in footage widely circulated on social media.
The White House did not dispute the authenticity of the video, which casts considerable doubt on the future of Iran's nuclear agreement, known as the JCPOA.
Struck in 2015 between Iran, China, France, Germany, Russia, the UK, US and EU, the landmark deal lifted crippling sanctions on the Iranian economy in exchange for limitations on Tehran's nuclear programme.
The video, which is circulating without a date or precise location, shows Biden speaking to people behind a metal barrier, one of whom has a headband in the colours of Iran on their forehead.
AFP report the footage corresponds to a campaign rally by Biden held in early November in California.
“President Biden, are you going to announce that the JCPOA is dead? Can you announce it?” a woman asks the US President, as he shakes her hand.
"He replies: It's dead but we will not announce it. It's a long story."
"We don't want an agreement with the mullahs...They don't represent us", adds the woman.
"I know they don't represent you. But they're going to have a nuke," says Biden, who is known for straying from official language, especially in informal chats.
"The president's comments are entirely consistent with what we're saying about the JCPOA, which is not our priority right now," said White House National Security Council spokesman John Kirby when asked about the video by reporters on Tuesday.
"We do not expect an agreement to occur in the near future," he repeated, avoiding using the same final wording as Biden.
"To my knowledge, no one is questioning the authenticity [of the video]," he added. "I don't think we are going to investigate it."
The JCPOA granted Iran relief from damaging international sanctions in exchange for guarantees that Tehran would not build atomic weapons, a goal the Islamic Republic has always denied.
In 2018, the US unilaterally withdrew from the international agreement, despite Iran's broad compliance with its terms. This led to the reinstatement of sanctions, with Tehran gradually reigning on its obligations.
Biden has pledged to try and resurrect the deal, but negotiations that started in April 2021 in Vienna have ground to a standstill.
Talks have been dogged by Tehran's violent suppression of protests beginning in September, alongside supplying drones to Russia.