The officials say that Israel must act by the summer if it wants to effectively attack Iran's programme.

A key question in the debate is how much damage Israel, or anyone else, can inflict - and whether it would be worth the risk of a possible counter-strike.

Israel contends a nuclear Iran would threaten its survival, citing Tehran's calls for the destruction of the Jewish state.

At the the World Economic Forum in Davos, Switzerland, Israeli Defence Minister Ehud Barak called for even tougher sanctions against Iran and said time was running out for the world to act.

"We are determined to prevent Iran from turning nuclear," he said. "It seems to us to be urgent, because the Iranians are deliberately drifting into what we call an immunity zone where practically no surgical operation could block them."

Back in Israel, Barak said: "We must not waste time on this matter. The Iranians continue to advance (towards nuclear weapons), identifying every crack and squeezing through. Time is urgently running out."

Key Israeli defence officials believe that the time to strike - if such a decision is made - would have to be by the middle of this year.

Complicating the task is the assessment that Iran is stepping up efforts to move its work on enriching uranium - a critical component of bombmaking - deep underground.

A team of UN nuclear inspectors, including senior weapons experts, is in Iran this week, and the findings from the visit could greatly influence Western efforts to expand economic pressures on Tehran over its uranium enrichment.

The European Union last month decided to stop importing oil from Iran - just weeks after the US approved, but has yet to enact new sanctions targeting Iran's Central Bank.