The head of Iran's elite Revolutionary Guards has warned that any Israeli or US attack on its nuclear sites would mean the outbreak of war, the official IRNA news agency reported on Friday.

"Any action against Iran will be interpreted as the start of a war," General Mohammad Ali Jafari was quoted as saying late on Thursday. "Iran's response to any military action will make the aggressors regret their decision."

The United States has never ruled out an eventual resort to force against Iran over its contested nuclear programme, which the West fears is cover for a drive to build an atomic weapon.

Israel, which is widely believed to be the Middle East's sole if undeclared nuclear power, has said it will stop Tehran from developing a nuclear bomb at all costs.

US media reported that more than 100 Israeli warplanes staged a training exercise with Greece last month to prepare for a possible long-distance strike and as a warning to Tehran.

Jafari warned Israel last week not to attack the Islamic republic, saying that the Jewish state was well within range of Iranian missiles.

Iran insists that its nuclear programme is peaceful and aimed only at energy production, vehemently denying allegations that it wants atomic weapons.

Currently under three sets of UN Security Council sanctions for its refusal to suspend sensitive uranium enrichment, Iran is set to respond to an offer of incentives by world powers aimed at resolving the nuclear standoff.

The country's top nuclear negotiator Saeed Jalili on Thursday expressed optimism that nuclear talks could start with world powers, but also stressed the importance of a package put forward by Tehran.

Iran's own package is a more all-embracing effort to solve global problems, and notably suggests the setting up of a consortium in Iran to enrich uranium.