"I actually am very hopeful that we don't get into a position where we have to get into a conflict," Adm. Michael Mullen, chairman of the Joint Chiefs of Staff, told Israel's Channel Ten television when asked if he might recommend that US forces strike Iranian nuclear facilities pre-emptively.

"It would be a very significant challenge for the United States right now to get into a third conflict in that part of the world," Mullen added, referring to the Bush administration's long-running military commitments in Iraq and Afghanistan.

Washington is leading efforts to curb Iran's nuclear plans through UN Security Council sanctions, but has also hinted that war could be a last resort for denying Tehran – which insists it seeks atomic energy only -- the means to make a bomb.

Jittery since Iranian President Mahmoud Ahmadinejad's 2005 call for the Jewish state to be "wiped off the map", Israeli officials have been lobbying for a tougher global stand against their arch-foe.

"I certainly share the concern about Iran and about the leadership, and I think it is very important that we increase as much as possible the financial pressure, the diplomatic pressure, the political pressure, and at the same time keep all the military options on the table," Mullen said.

Believed to have the Middle East's only atomic arsenal, Israel bombed Iraq's nuclear reactor in 1981. Israeli warplanes also destroyed a site in Syria last September, which U.S. officials said was that of a secret nuclear programme, though Damascus denied having any such facility.

"Certainly the situation with Syria is a troubling one and the development of this nuclear reactor was a troubling one indeed, and it is also indicative of what can be done out of the sight of people," Mullen said.

"You just can't be sure whether someone isn't developing one somewhere else."