Israel "will attack" Iran if it continues to develop nuclear weapons, one of prime minister Ehud Olmert's deputies warned yesterday. Shaul Mofaz, a former defence minister and a contender to replace the scandal-battered Olmert, said military action would be "unavoidable" if Tehran proved able to acquire the technology to manufacture atomic bombs.

Mofaz is Israel's transport minister, but he is also a former chief of staff, privy to secret defence planning as a member of the security cabinet, and leads regular strategic talks with the US. He implied that any attack on Iran would be coordinated with Washington. "If Iran continues with its programme for developing nuclear weapons, we will attack it," he told the Hebrew daily Yediot Aharonot. "The UN sanctions are ineffective."

Mofaz was born in Iran, giving his remarks extra edge after repeated threats against Israel from President Mahmoud Ahmadinejad, who has also denied the Nazi Holocaust. Ahmadinejad "would disappear before Israel does", Mofaz said.

Mofaz's remarks came at the end of a week of intense US-Israeli talks on Iran. They were also the most explicit threat yet against the Islamic Republic from a member of the Israeli government, which, like the Bush administration, has preferred to hint at force as a last resort should UN sanctions be deemed to have failed.

Barack Obama, the Democratic presidential candidate, told pro-Israeli lobbyists this week that the military option against Iran remained on the table, though he also offered "meaningful concessions" if it bowed to international demands.

Ehud Barak, the defence minister and Labour party leader, said Israel needed to do everything possible to ensure that the Iranians did not obtain nuclear power.

Javier Solana, the EU foreign policy chief, is shortly to lead a team of high-ranking diplomats from Britain, France, Russia, China and Germany, who will present a package of incentives to persuade Tehran to suspend uranium enrichment. Iran has rejected it in advance.

Experts doubt whether Israel could destroy Iran's extensive and heavily defended nuclear facilities without American help. In 1981 Israel bombed and destroyed Iraq's nuclear reactor. Last September its planes bombed a site in Syria that the US said was a nuclear reactor built with North Korean help. Syria denied having any such facility. Israel is believed to have an arsenal of 150-400 nuclear warheads. Unlike Iran, it has never signed the nuclear non-proliferation treaty.

Iran denied seeking to develop nuclear weapons and insisted it would not abandon enrichment. But the International Atomic Energy Agency, the UN's nuclear watchdog, has demanded "full disclosure" from Tehran over allegations that it covertly studied how to design a nuclear weapon. Iran has dismissed intelligence on this as baseless, forged or irrelevant.