The Israeli Defence Minister, Shaul Mofaz, warned on Wednesday that Iran will reach "the point of no return" within the next 12 months in its covert attempt to secure a nuclear weapons capability.

Tehran denies pursuing a nuclear weapons programme.

Speaking in London before a meeting on Thursday with British Prime MinisterTony Blair, Lieutenant General Mofaz said Iran was the main long-term threat to the world and stressed that it will not be permitted to build a nuclear bomb. "None of the western countries can live with Iran having a nuclear capability," he told reporters.

General Mofaz, a hawk in the Israeli Cabinet, who has said in the past that Israel has operational plans in place for a strike against Iranian nuclear facilities, refused to rule out military action.

Blair, speaking in the Commons on Wednesday, said the Iranian issue was serious. Asked by the former Labour minister, Michael Meacher, to give an "unequivocal and categorical assurance" that Britain would not take part in any attack on Iran, Blair said: "I know of no such contemplation by the United States of America."

In an interview with The Financial Times on Wednesday, Blair refused to rule out the option of using military force.

With the US bogged down in the Iraq conflict, opening another front in Iran would be risky. Iran's Shebab-3 rockets are theoretically capable of hitting Israel.

The Israeli and US rhetoric has grown more strident in the last week and could be aimed at pushing Britain, France and Germany into taking a tougher diplomatic approach towards Iran.

The US Vice-President, Dick Cheney, said last week that Israel might launch a pre-emptive strike on Iran's nuclear facilities, as it did against Iraq's nuclear reactor at Osirak in 1981.

General Mofaz indicated on Wednesday that he thought the US rather than Israel should do it: "It is the strongest power that can stop any nuclear power, especially in the hands of an extreme regime."

US officials have confirmed privately a report by the US reporter, Seymour Hersh, in the New Yorker, that US special forces have already been in Iran scouting out its nuclear facilities.

General Mofaz, who was born in Iran but left for Israel while a child, said: "Iran is very close to the point of no return, which means the enrichment of uranium, and we believe that the leadership of the US, together with the European countries, should stop as soon as possible this military nuclear programme in Iran."

He added that this point of no return would be reached "in less than a year" and that it would only be "a matter of years" after that that it would assemble the bomb .

The Israeli intelligence assessment, shared by the US and Britain, is that Iran could have a bomb by 2007.

The foreign secretary, Jack Straw, flew with his German and French counterparts to Tehran late in 2003 to broker a deal with Iran to suspend its enrichment programme. The deal broke down last year when the troika accused Iran of reneging on the deal. A new round of negotiations is under way and expected to drag on for at least a few months.

Like the US, which is equally sceptical, Israel is pushing for the issue to be referred to the United Nations for the imposition of sanctions and deep inspections by UN staff of Iran's nuclear facilities.

General Mofaz's comment about "point of no return" echoed a private briefing by Meir Dagan, the head of the Israeli overseas intelligence service, Mossad, to members of the Knesset on Monday. Dagan said Cheney's remark that Israel might make a pre-emptive strike was aimed at pressing Europe to adopt the tougher US approach towards Iran.

Britain, France and Germany have switched to a harder approach towards Iran. A confidential EU document leaked to Reuters and confirmed independently said the troika had told Iran it would be "unacceptable" for Tehran to keep its uranium enrichment programme, even if, as it claims, it is solely for civil purposes.

The commander of the Iranian Revolutionary Guard ground forces, Brigadier General Mohammad Ali Jafari, said on Wednesday: "Iran will retaliate against any stupid moves by Israel." - Guardian Unlimited © Guardian Newspapers Limited 2005