The US intelligence chief said on Tuesday that Iran is still undecided on whether to make a nuclear bomb though it has the ability.
"There is dissension and debate in the political hierarchy of Iran (over whether to build a nuclear weapon)," US Director of National Intelligence James Clapper told a hearing held by the Senate Intelligence Committee.
While weighing the pros and cons of making a nuclear weapon, Iranian politicians have not yet reached "unanimity" on the issue, he said, adding that though Iran is capable of producing a nuclear weapon, the Islamic Republic is not building one right now, reported Xinhua.
Clapper also said Iran is more likely to respond with an attack on the US.
The new US sanctions would have a great impact on Iran, but they were not likely to result in the fall of its regime, he said.
CIA Director David Petraeus, who testified at the same hearing, said new sanctions on Iran "have been biting much, much more in recent weeks", but it remained to be seen whether this could force Iran to change its behaviour and policy on its nuclear programme.
On Dec 31, US President Barack Obama signed a bill with provisions asking for new sanctions on Iran, targeting foreign financial institutions that do business with Iran's central bank, the main conduit for its oil revenues.
The move, aimed at choking off Iran's critical oil income, prompted furious reactions from the Islamic Republic, which has threatened to close the Strait of Hormuz, one of the world's most critical oil routes.
US Defense Secretary Leon Panetta said Washington would "not tolerate" the blocking of the Strait of Hormuz and Iran's production of a nuclear weapon. He stressed that they were two "red lines", and the US would respond if Iran crossed them.