Dec
 22 (Reuters) - The Biden administration is concerned that a weakened 
Iran could build a nuclear weapon, White House National Security Adviser
 Jake Sullivan said on Sunday, adding that he was briefing 
President-elect 
Donald Trump's team on the risk.
Iran has suffered setbacks
 to its regional influence after Israel's assaults on its allies, 
Palestinian Hamas and Lebanon's Hezbollah, followed by the fall of 
Iran-aligned Syrian President 
Bashar al-Assad.
 Israeli strikes
 on Iranian facilities, including missile factories and air defenses, 
have reduced Tehran's conventional military capabilities, Sullivan told 
CNN.
 "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 said.
Iran
 says its nuclear program is peaceful, but it has expanded uranium 
enrichment since Trump, in his 2017-2021 presidential term, pulled out 
of a deal between Tehran and world powers that put restrictions on 
Iran's nuclear activity in exchange for sanctions relief.
Sullivan said that there was a risk that Iran might abandon its promise not to build nuclear weapons.
"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.
Trump, who takes office on Jan. 20, could return to his hardline Iran policy by stepping up sanctions on Iran's oil industry.
Sullivan said Trump would have an opportunity to pursue diplomacy with Tehran, given Iran's "weakened state."
"Maybe
 he can come around this time, with the situation Iran finds itself in, 
and actually deliver a nuclear deal that curbs Iran's nuclear ambitions 
for the long term," he said.
Reporting by Simon Lewis; Editing by Mark Porter and Lisa Shumaker