WASHINGTON: A US military attack on Iran would do more damage than a strike carried out by Israeli forces, Defense Secretary Leon Panetta said Thursday in an interview.

The United States and Israel disagree about the imminence of the threat posed by Iran's nuclear program, and Panetta's comments underscored the US administration's stance that Israel should hold off on any unilateral action.

“If they (Israelis) decided to do it, there's no question that it would have an impact, but I think it's also clear that if the United States did it, we would have a hell of a bigger impact,” Panetta told the National Journal.

President Barack Obama and top officials have repeatedly said they have not ruled out military force if diplomacy and sanctions fail to resolve the crisis over Iran's suspect nuclear program.But the Obama administration maintains that tough sanctions on Iran and diplomatic efforts need to be given more time before any resort to bombing raids.

Israeli leaders however say time is running out for any pre-emptive strike.

Prime Minister Benjamin Netanyahu said on Monday that sanctions against Iran have not worked, and “none of us can afford to wait much longer.”US commanders have said the military has drawn up contingency plans for a potential attack on Iran's nuclear facilities and Panetta confirmed that in the interview.

Asked if the Pentagon was drawing up contingency plans, he said:

“Absolutely. Analysts and former US military officers say Israeli aircraft could do serious damage to Iran's nuclear sites but would face a challenge hitting an underground facility near Qom and that America's vast air force far outstrips Israel's capabilities."

The United States, Israel and much of the international community fear Iran's nuclear program is an attempt to build a weapon — a charge Tehran denies.