PENTAGON chiefs fear that Israeli plans for an attack on Iran's nuclear program will fail to destroy the facilities because neither the CIA nor Mossad knows where every base is located.

US commanders fear Israel will feel compelled to act within 12 months, with no guarantee that it can do more than slow Iran's development of a nuclear weapon.

Gaps in intelligence on the precise location and the vulnerabilities of Iran's facilities emerged during recent talks between Admiral Mike Mullen, the US chairman of the Joint Chiefs of Staff, and Israeli generals.

The assessment emerged as Iran in effect thumbed its nose at proposals by the West for Tehran to freeze its uranium enrichment program in exchange for the easing of economic sanctions. In its reply sent to the European Union's foreign policy chief, Javier Solana, Iran said it was prepared to negotiate, but only from a position of equality, and made no reference to the specific proposals.

"Iran will not go back on its rights on the nuclear issue," said a Government spokesman, Gholamhossein Elham. "The will of the Iranian people is firm and will continue to follow the principles defined by the supreme guide [Ayatollah Ali Khamenei]."

"Iran insists on negotiations [with world powers] while respecting its rights and avoiding any loss of international rights," he said, referring to Tehran's refusal to give up on nuclear enrichment.

At the same time General Mohammed al-Jafari, the head of the Iranian Revolutionary Guard, warned that any attack on Iran would be "regarded as the beginning of war".

A former head of Mossad, the Israeli agency whose main responsibility is overseas intelligence, said last week that Israel would have to act within a year to prevent Iran securing nuclear weapons.

Those familiar with the Israeli-American military talks believe that Israel is still determined to act before Iran has enough highly enriched uranium to build a bomb, and before Tehran has acquired the Russian SA-20 air defence system to protect its nuclear facilities.

"The Israelis have a real sense of urgency," an official familiar with the discussions said. "They are stepping up their preparations. But the Israelis and the Americans are worried about each other's lack of intelligence.

"The Americans had spies in Iran until they were rounded up in 2003 and now they do not have much by way of [human intelligence] on the ground. The Israelis have better information. But the Americans went away from the meetings unconvinced that the Israelis have enough intelligence on where to strike, and with little confidence that they will be able to destroy the nuclear program."

The shortage of good intelligence could explain reports that the US President, George Bush, has sanctioned a dramatic increase in covert operations by US special forces troops inside Iran. These intelligence gaps lay behind Admiral Mullen's decision to speak out on Wednesday against military action, saying it would be "extremely stressful" to "open a third front" in the "war on terror". The admiral is at odds with hawks in the Administration, led by the Vice-President, Dick Cheney.

A former CIA officer with 30 years of Iranian experience said: "The US would get the blame from Iran whether or not we play a major role in any attack, so we might as well do the job properly."

Telegraph, London; Agence France-Presse