It is using hitmen, sabotage, front companies and double agents to disrupt the regime's illicit weapons project, the experts say. The most dramatic element of the "decapitation" programme is the planned assassination of top figures involved in Iran's atomic operations.

Despite fears in Israel and the US that Iran is approaching the point of no return in its ability to build atom bomb, Israeli officials are aware of the change in mood in Washington since President Barack Obama took office.

They privately acknowledge the new US administration is unlikely to sanction an air attack on Iran's nuclear installations and Mr Obama's offer to extend a hand of peace to Tehran puts any direct military action beyond reach for now.

The aim is to slow down or interrupt Iran's research programme, without the gamble of a direct confrontation that could lead to a wider war.

A former CIA officer on Iran told The Daily Telegraph: "Disruption is designed to slow progress on the programme, done in such a way that they don't realise what's happening. You are never going to stop it.

"As US-Israeli relations are bound to come under strain over the Obama administration's outreach to Iran, and as the political atmosphere grows in complexity, an intensification of Israeli covert activity against Iran is likely to result."