The Biden administration is concerned that a weakened Iran could decide to build a nuclear weapon, White House National Security Adviser Jake Sullivan said on Sunday, adding that he was briefing incoming President-elect Donald Trump's team on the risk.

Iran is reeling from setbacks to its regional influence after Israel's assaults on its allies, Palestinian Hamas and Lebanon's Hezbollah, followed by the fall of Syrian Iran-aligned President Bashar al-Assad.

Tehran's "conventional capabilities" have also been reduced, Sullivan told CNN, a reference to recent Israeli strikes on Iranian facilities, including missile factories and air defenses.

"It's no wonder there are voices (in Iran) saying 'Hey, maybe we need to go for a nuclear weapon right now... Maybe we have to revisit our nuclear doctrine'," Sullivan told CNN.

Iran says its nuclear program is peaceful, but has expanded uranium enrichment since Trump in his first term as president pulled out of a deal between Iran and world powers to curb Tehran's nuclear ambitions.

Sullivan said there is now a "real risk" that Iran will revise its position that "we're not going for a nuke."

"It's a risk we are trying to be vigilant about now. It's a risk that I'm personally briefing the incoming team on," Sullivan said, adding that he had also consulted with U.S. ally Israel on the issue.

Trump, who takes power on Jan. 20, is likely to step up sanctions on Iran's oil industry despite calls to return to negotiations from critics who see diplomacy as a more effective long-term policy.