Israeli jet pilots trained for a possible strike on Iranian nuclear sites, according to reports in the US media.
It has sparked a strong warning from Tehran and caution from world leaders.
A major military exercise carried out by Israel earlier this month seemed to be a test-run for any potential strike against Iran's nuclear facilities, the New York Times reported, citing US officials.
The manoeuvres, code-named 'Glorious Spartan 08,' took place on 28 May and 12 June and consisted of aerial manoeuvres and knowledge exchange.
The goal was for more than 100 Israeli F-16 and F-15 fighter jets to prepare for long-range strikes and demonstrate Israel's serious concern over Iran's nuclear ambitions, the Times reported.
On 6 June Israeli Deputy Prime Minister Shaul Mofaz warned that Iran would face attack if it pursues what he said was its nuclear weapons program.
In Tehran, senior cleric Ayatollah Ahmad Khatami warned Israel of a 'strong blow' if it attacks Iran.
At the United Nations, US ambassador Zalmay Khalilzad said that Washington favoured diplomacy to resolve the Iranian nuclear crisis at least for the moment.
The UN Security Council has in the last two years imposed three rounds of increasingly stiff sanctions on Iran for its decision to spurn the incentives and continue pursuing its enrichment program.
Russian Foreign Minister Sergei Lavrov said in a Moscow speech that there was no proof Iran is developing nuclear weapons, and warned unilateral action risked repeating the mistakes of the Iraq invasion.
