"The bottom line: we think it's a couple of years away in that regard. It could be more, could be a little bit less," General David Petraeus, the head of the US Central Command, said in interview on CNN.
"There are certainly a lot of facts that we don't know about what goes on inside Iran," he added.
The United States and its European allies fear that Tehran intends to acquire a nuclear weapon under the cover of a civilian nuclear program, which Iran denies.
But Petraeus noted that to acquire a weapon, Iran must have enough highly enriched uranium, must make a warhead and have long-range missiles capable of delivering them. US intelligence believes Iran halted a secret program to design a nuclear weapon in 2003.
On the other hand, the head of Israeli military intelligence, Major General Amos Yadlin, predicted last week that Iran will have the capacity to build a nuclear weapon within a year but is not rushing to produce one.
"The Iranian strategy is not to get a nuclear bomb as soon as they can so as not to give the world a reason to act against them," Yadlin told the Israeli parliament.
