Israel has drawn up secret plans to destroy Iran's uranium enrichment facilities with tactical nuclear weapons, Britain's Sunday Times newspaper said.

Citing what it said were several Israeli military sources, the paper said two Israeli air force squadrons had been training to blow up an enrichment plant in Natanz using low-yield nuclear "bunker busters".

Two other sites, a heavy water plant at Arak and a uranium conversion plant at Isfahan, would be targeted with conventional bombs, the Sunday Times said.

The U.N. Security Council voted unanimously last month to slap sanctions on Iran to try to stop uranium enrichment that Western powers fear could lead to making bombs. Tehran insists its plans are peaceful and says it will continue enrichment.

Israel has refused to rule out pre-emptive military action against Iran along the lines of its 1981 air strike against an atomic reactor in Iraq, though many analysts believe Iran's nuclear facilities are too much for Israel to take on alone.

The newspaper said the Israeli plan envisaged conventional laser-guided bombs opening "tunnels" into the targets. Nuclear warheads would then be used fired into the plant at Natanz, exploding deep underground to reduce radioactive fallout.

Israeli pilots have flown to Gibraltar in recent weeks to train for the 2,000 mile (3,200 km) round-trip to the Iranian targets, the Sunday Times said, and three possible routes to Iran have been mapped out including one over Turkey.

However it also quoted sources as saying a nuclear strike would only be used if a conventional attack was ruled out and if the United States declined to intervene. Disclosure of the plans could be intended to put pressure on Tehran to halt enrichment, the paper added.

Washington has said military force remains an option while insisting that its priority is to reach a diplomatic solution.

Iran's President Mahmoud Ahmadinejad has called for Israel to be "wiped off the map". Israel, widely believed to have the Middle East's only nuclear arsenal, has said it will not allow Iran to acquire nuclear weapons.