Israel itself has neither confirmed nor denied the exercises, with an Israeli military spokesman saying only that the country's air force "regularly trains for various missions in order to confront and meet the challenges posed by the threats facing Israel".

Israel and Western powers have accused Iran of attempting to acquire nuclear weapons, however Iran says its nuclear programme is solely for peaceful purposes.

Sean McCormack, the US state department spokesman, did not comment on the claims but said that Washington supported "a peaceful, diplomatic resolution" to the crisis.

However, Mohamed ElBaradei, the head of the International Atomic Energy Agency (IAEA), the United Nation's nuclear watchdog, said that if a military strike were carried out on Iran he would resign, earning that such an act would turn the region "into a fireball".

"I don't believe that what I see in Iran today is a current, grave and urgent danger. If a military strike is carried out against Iran at this time ... it would make me unable to continue my work," ElBaradei told Al Arabiya television.

"A military strike, in my opinion, would be worse than anything possible. It would turn the region into a fireball."

'Significant' exercise

The New York Times quoted defence department officials as saying that more than 100 Israeli F-16s and F-15s took part in the exercises, flying more than 1,450 kilometres - roughly the distance from Israel to Iran's Natanz nuclear enrichment facility.

The exercises also reportedly included refueling tankers and helicopters capable of rescuing downed pilots.

"It was noticed that a significant exercise took place - dozens and dozens of aircraft participated,'' one US official told AP.

"We watch globally everyday, and this was noted."

On Friday, Sergey Lavrov, the Russian foreign minister, said that Iran should be engaged in dialogue and warned against unilateral military action.

"I hope the actual actions [over Iran's nuclear programme] would be based on international law," he said.

"International law clearly protects Iran's and anyone else's territorial integrity."

'Defending itself'

Ehud Olmert, the Israeli prime minister, has said he favours a diplomatic solution to the Iranian nuclear crisis but has not ruled out military action and neither has George Bush, the US president.

Olmert told a German newspaper on Friday that there were "many things" that could be done economically, politically, diplomatically and militarily.''

Israel "always has to be in a position to defend itself against any adversary and against any threat of any kind".

In 1981, Israeli jets bombed the Osirak nuclear facility in Iraq to thwart Saddam
Hussein's nuclear programme.

And last September Israel bombed a facility in Syria that US officials have alleged was a nuclear reactor being constructed with North Korean help.