Tehran today denounced Israel as a "threat to global peace" after Israel held a large military exercise in an apparent dress rehearsal for a potential attack on Iranian nuclear facilities.
An Iranian government spokesman, Gholam-Hossein Elham, dismissed suggestions of an attack by Israel as "impossible", the official IRNA news agency reported.
He said "the threats and the claims of [the] Zionist regime" proved Iran's view that Israel was "dangerous and a threat to the global peace and security".
Elham's remarks came after Pentagon officials confirmed US media reports of a large military exercise by Israel earlier this month to show Iran that it had the capacity to strike at its nuclear facilities.
More than 100 Israeli F-16s and F-15s flew more than 900 miles in the Mediterranean, roughly the distance from Israel to Iran's Natanz nuclear plant. They were accompanied by refuelling planes and helicopters for rescuing any downed crews.
A source in Washington described the exercise as "sabre-rattling" and said he did not think an attack was imminent.
"If the Israelis were serious about it, no one would know about it until after it has happened," he said.
Nonetheless, the development sent oil prices higher after it was leaked to the New York Times by the Pentagon.
Mohamed ElBaradei, head of the International Atomic Energy Agency, responded to the news by saying an attack would turn the region into a "fireball" adding that he would resign if there were a military strike.
Both the US and Israel have said they will not allow Iran to secure a nuclear weapon capability. Iran says its nuclear development is for civilian purposes and it has no ambition to build a bomb.
Sergei Lavrov, Russia's foreign minister, warned Israel and the US against any attack, saying there was no evidence that Iran was intent on building a nuclear weapon. Asked about Israeli warnings this month, Lavrov said yesterday: "I hope the actual actions would be based on international law. And international law clearly protects Iran's and anyone else's territorial integrity."
Pentagon officials told reporters that the Israelis "have been conducting some large-scale exercises - they live in a tough neighbourhood".
The leak came a week after Javier Solana, the EU foreign policy chief, offered a deal to Tehran to stop uranium enrichment, a stage in the development of a nuclear weapon capability. Tehran has not ruled it out.
The leak could be designed to put pressure on Iran - but it may be counterproductive, pushing Tehran into rejection. Two days after the offer, while George Bush was visiting London, Gordon Brown announced tougher financial sanctions against Iran.
There has long been speculation that Bush, prodded by Dick Cheney, the US vice-president, might launch an attack - or give the green light to Israel to launch one - before leaving office next January. But that speculation is receding.
The Israeli military refused to comment on the exercise but said its air force "regularly trains for various missions in order to confront and meet the challenges posed by the threats facing Israel".
Although Israel says it favours tougher sanctions to curb Iranian nuclear ambitions, it has pointedly not ruled out military action.
This week, Ehud Olmert, the prime minister, repeated his warning that Iran remained the biggest threat in the region. "I don't think we deserve to live under the threat of a nuclear Iran," he said in an interview with the Sydney Morning Herald published on Thursday.
Shaul Mofaz, a deputy prime minister and former army chief, provoked criticism this month when he told an Israeli newspaper that an attack was unavoidable. "If Iran continues its programme to develop nuclear weapons we will attack it," said Mofaz, who is in charge of Israel's strategic dialogue with the US over such issues as Iran.
But some analysts suggested Mofaz was not reflecting a government decision but simply positioning himself ahead of possible leadership elections within Israel.
In recent weeks, Israel has appeared to take a less confrontational approach on some issues. On Thursday a ceasefire went into effect with Hamas in Gaza, even though Israel has long said it would not negotiate with the Islamist group. The government has begun indirect talks with Syria for the first time in eight years, and a prisoner swap with Hizbullah is reportedly near. Israel has also called for direct talks with Lebanon.
Martin Van Creveld, a military analyst at Jerusalem's Hebrew University, said preparations for a possible attack were under way. "Israel has been talking about this possibility for a long time, that it would not take an Iranian nuclear weapon lying down."