At least 20 heads of mission and other top diplomats have been sacked or reassigned in the biggest shake-up since the Iranian Revolution of 1979. The majority were appointed during the decade of rapprochement with the West that Mr Ahmadinejad has abruptly reversed.

Four of the envoys, the ambassadors to London, Paris, Berlin and the representative to the United Nations in Geneva, were involved in months of delicate mediation between Iran and Europe over Tehran’s nuclear programme.

Iranian and Western officials told The Times that they feared the purge was a sign of a further hardening of the provocative foreign policy that has isolated Mr Ahmadinejad’s regime.

One of the most prominent victims of the diplomatic cull is Mohammad Hossein Adeli, the urbane, American-educated Ambassador to London, who has served only for 12 months and is the first Iranian envoy since the Islamic Revolution who speaks fluent English.

Mr Adeli, 52, will be leaving the foreign service in the coming weeks, along with the Iranian envoys to Paris, Berlin, Geneva and Kuala Lumpur. Iran’s ambassadors to Indonesia, Kazakhstan and several Arab states are also believed to be on the hitlist.

“We are expecting Iran to recall more than 20 ambassadors and heads of mission,” a Western diplomat in Tehran told The Times. “Obviously the new Government wants to have its own people and many of these ambassadors were supporters of (the former President) Rafsanjani and were pro-reform.”

Whatever the domestic political reasons behind the dismissals, it could not come at a worse time for Iran’s standing abroad. Last week the international community reacted with outrage when Mr Ahmadinejad called for Israel to be “wiped off the map”. Several of the ambassadors being recalled had to deal with the fallout from the remarks when they were summoned to receive protests from host governments.

In September Mr Ahmadinejad, a former commando in the Iranian Revolutionary Guards and former Mayor of Tehran, used similarly tough language during his first UN speech Instead of courting the international community, he warned foreigners not to meddle in Iran’s affairs, particularly its nuclear programme, which many fear could be a cover for building an atomic bomb.

That issue is likely to dominate a meeting of the International Atomic Energy Agency (IAEA) board of governors scheduled for this month, and Iran could face sanctions if its case is referred to the UN Security Council.

Now, however, many of the country’s most qualified diplomatic negotiators will be out of work. They include Mohammad Reza al-Borzi, Iran’s envoy to the UN in Geneva, who has been a key intermediary with Britain, France and Germany over the nuclear issue.

“This is an enormous mistake. The regime has shot itself in the foot,” said Dr Ali Ansari, an Iranian expert at St Andrews University. “It is typical of the insularity of the regime that it creates this crisis and gets rid of its best diplomats just at a time when things could not be worse on the world stage.”

It is still not clear who will replace the ambassadors. In Britain’s case Tehran may choose to leave the post vacant in protest at a recent dispute over Iraq that has already prompted an informal boycott of British goods sold to Iran.

It is clear that a very different type of diplomat is likely to emerge from the shake-up. For instance, Mounacher Mottaki, the new Foreign Minister, is a former Ambassador to Japan and Turkey who was expelled from Ankara after being accused of supporting attacks against Iranian dissidents.

He is a close ally of Ali Lari-jani, the powerful, hardline new secretary of the Supreme National Security Council, in charge of Iran’s nuclear negotiations and policy on Iraq.

But the hardening of Iranian policy is not going unchallenged at home. Mr Ahmadinejad may have won a landslide victory but he still has powerful opponents.

Mohammad Khatami and Akbar Hashemi Rafsanjani, two former reformist presidents, are openly critical of his policies. On Sunday, Mr Khatami accused the new leader of “using fascist values and principles in the name of Islam to criticise liberalism”. Mohammad Atrianfar, a close Rafsanjani ally, yesterday called the sackings a big diplomatic mistake. “The President does not understand that he should proceed with caution,” he said.

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