The order came after Israeli intelligence warned the government that Iran was operating enrichment facilities, believed to be small and concealed in civilian locations.

Iran’s stand-off with the International Atomic Energy Agency (IAEA) over nuclear inspections and aggressive rhetoric from Mahmoud Ahmadinejad, the Iranian president, who said last week that Israel should be moved to Europe, are causing mounting concern.

The crisis is set to come to a head in early March, when Mohamed El-Baradei, the head of the IAEA, will present his next report on Iran. El-Baradei, who received the Nobel peace prize yesterday, warned that the world was “losing patience” with Iran.

A senior White House source said the threat of a nuclear Iran was moving to the top of the international agenda and the issue now was: “What next?” That question would have to be answered in the next few months, he said.

Defence sources in Israel believe the end of March to be the “point of no return” after which Iran will have the technical expertise to enrich uranium in sufficient quantities to build a nuclear warhead in two to four years.

“Israel — and not only Israel — cannot accept a nuclear Iran,” Sharon warned recently. “We have the ability to deal with this and we’re making all the necessary preparations to be ready for such a situation.”

The order to prepare for a possible attack went through the Israeli defence ministry to the chief of staff. Sources inside special forces command confirmed that “G” readiness — the highest stage — for an operation was announced last week.

Gholamreza Aghazadeah, head of the Atomic Organisation of Iran, warned yesterday that his country would produce nuclear fuel. “There is no doubt that we have to carry out uranium enrichment,” he said.

He promised it would not be done during forthcoming talks with European negotiators. But although Iran insists it wants only nuclear energy, Israeli intelligence has concluded it is deceiving the world and has no intention of giving up what it believes is its right to develop nuclear weapons.

A “massive” Israeli intelligence operation has been underway since Iran was designated the “top priority for 2005”, according to security sources.

Cross-border operations and signal intelligence from a base established by the Israelis in northern Iraq are said to have identified a number of Iranian uranium enrichment sites unknown to the the IAEA.

Since Israel destroyed the Osirak nuclear reactor in Iraq in 1981, “it has been understood that the lesson is, don’t have one site, have 50 sites”, a White House source said.

If a military operation is approved, Israel will use air and ground forces against several nuclear targets in the hope of stalling Tehran’s nuclear programme for years, according to Israeli military sources.

It is believed Israel would call on its top special forces brigade, Unit 262 — the equivalent of the SAS — and the F-15I strategic 69 Squadron, which can strike Iran and return to Israel without refuelling.

“If we opt for the military strike,” said a source, “it must be not less than 100% successful. It will resemble the destruction of the Egyptian air force in three hours in June 1967.”

Aharon Zeevi Farkash, the Israeli military intelligence chief, stepped up the pressure on Iran this month when he warned Israel’s parliament, the Knesset, that “if by the end of March the international community is unable to refer the Iranian issue to the United Nations security council, then we can say the international effort has run its course”.

The March deadline set for military readiness also stems from fears that Iran is improving its own intelligence-gathering capability. In October it launched its first satellite, the Sinah-1, which was carried by a Russian space launcher.

“The Iranians’ space programme is a matter of deep concern to us,” said an Israeli defence source. “If and when we launch an attack on several Iranian targets, the last thing we need is Iranian early warning received by satellite.”

Russia last week signed an estimated $1 billion contract — its largest since 2000 — to sell Iran advanced Tor-M1 systems capable of destroying guided missiles and laser-guided bombs from aircraft.

“Once the Iranians get the Tor-M1, it will make our life much more difficult,” said an Israeli air force source. “The installation of this system can be relatively quick and we can’t waste time on this one.”

The date set for possible Israeli strikes on Iran also coincides with Israel’s general election on March 28, prompting speculation that Sharon may be sabre-rattling for votes.

Benjamin Netanyahu, the frontrunner to lead Likud into the elections, said that if Sharon did not act against Iran, “then when I form the new Israeli government, we’ll do what we did in the past against Saddam’s reactor, which gave us 20 years of tranquillity”.

TEHRAN MINISTER MET MILITANTS BEFORE NEW OFFENSIVE

Iran’s foreign minister met leading figures from three Islamic militant groups to co-ordinate a united front against Israel days before a recent escalation of attacks against Israeli targets shattered fragile ceasefires with Lebanon and the Palestinians, writes Hugh Macleod in Damascus.

The minister, Manouchehr Mottaki, held talks with leaders of Hamas, Islamic Jihad and Hezbollah in Damascus on November 15.

Among those who attended the meeting were Khaled Meshaal, the Hamas leader, and a deputy leader of Islamic Jihad, which claimed responsibility for last Monday’s suicide bombing of a shopping mall in Netanya that killed five Israeli citizens.

Ahmed Jibril, leader of the Popular Front for the Liberation of Palestine- General Command, was also present. “We all confirmed that what is going on in occupied Palestine is organically connected to what is going on in Iraq, Syria, Iran and Lebanon,” said Jibril.

Seven days after the talks, Hezbollah fired a volley of rockets and mortars at Israeli targets, sparking the fiercest fighting between the two sides since Israel’s withdrawal from south Lebanon five years ago.