Its ballistic missile programme suffered a major setback on Nov 12 after an explosion at the regime’s main missile testing facility at Bidganeh, about 30 miles west of Tehran.

At least 17 people died, including Gen Hassan Tehrani Moghaddam, the head of Iran’s missile research programme.

The IAEA report said Iranian scientists had worked to develop a missile capable of carrying nuclear warheads. Security analysts described Iran’s missile advances as “a turning point” that had “profound strategic implications”.

Last week another mysterious explosion caused significant damage to Iran’s uranium conversion facility at Isfahan.

“It looks like the 21st century form of war,” said Patrick Clawson of the Washington Institute for Near East Policy, a Washington think tank, told the Los Angeles Times. “It does appear that there is a campaign of assassinations and cyber war, as well as the semi-acknowledged campaign of sabotage.”

Ayatollah Ali Khamenei, Iran’s spiritual leader, issued a directive to the heads of all the country’s military, intelligence and security organisations to take all necessary measures to protect the regime.

Gen Jaafari responded to this directive by ordering Revolutionary Guards units to redistribute Iran’s arsenal of long-range Shahab missiles to secret sites around the country where they would be safe from enemy attack and could be used to launch retaliatory attacks.

In addition, the Iranian air force has formed a number of “rapid reaction units”, which have been carrying out extensive exercises to practice a response to an enemy air attack.

At the weekend, Iran claimed it had succeeded in shooting down an advanced American RQ-170 drone in the east of the country. If true, this would represent a major coup for the ayatollahs, as this type of drone contains sensitive stealth technology that allows it to operate for hours without being detected.

A spokesman for Nato’s International Security Assistance Force in Afghanistan would only confirm that US operators had “lost control” of a drone, without specifying the model.

Intelligence officials believe the dangerous game of cat and mouse between Iran and the West was responsible for last week’s attack on the British Embassy in Tehran. William Hague, the Foreign Secretary, closed the embassy and expelled Iranian diplomats in response.

But with Iran showing no sign of backing down over its nuclear programme, there is growing concern that Israel will launch unilateral military action.

At the weekend, Benjamin Netanyahu, Israel’s prime minister, warned that he would take “the right decision at the right moment” if Iran continued with its uranium enrichment programme.

Israel’s uncompromising approach is viewed with alarm in Washington.

Leon Panetta, the US defence secretary, has warned that a unilateral strike by Israel risked “an escalation” that could “consume the Middle East in confrontation and conflict that we would regret”.

A senior Western intelligence official said: "There is deep concern within the senior leadership of the Iranian regime that they will be the target of a surprise military strike by either Israel or the US.

"For that reason they are taking all necessary precautions to ensure they can defend themselves properly if an attack happens."