It remained unclear whether Israel was genuinely poised to strike or if it was sabre-rattling to prod the international community into taking a tougher line on Iran.
Israeli leaders have long hinted at a military option, but they always seemed mindful of the practical difficulties, the likelihood of a furious counter-strike and the risk of regional mayhem.
The developments unfolded as the International Atomic Energy Agency prepares to focus on the Iranian programme at a meeting later this month.
The West wants to set a deadline for Iran to start co-operating with an agency inquiry into suspicions that Tehran is secretly experimenting with components of a weapons programme.
Israeli leaders have said they favour a diplomatic solution, but recent days have seen a spate of Israeli media reports on a possible strike, accompanied by veiled threats from top politicians.
In a speech to parliament this week, Mr Netanyahu said a nuclear-armed Iran would pose a “dire threat” to the world and “a grave, direct threat on us, too”.
His hawkish foreign minister, Avigdor Lieberman, was dismissive of the reports but added: “We are keeping all the options on the table.”
The government official confirmed a report in the Haaretz daily that Mr Netanyahu and Defence Minister Ehud Barak both favour an attack, but do not yet have the support of a majority of cabinet ministers.
The official said Israel’s top security chiefs, including the heads of the military and Mossad spy agency, oppose military action.
Iran’s military chief, General Hasan Firouzabadi, vowed fierce retaliation if it was attacked. “We are fully prepared to use our proper equipment to punish any mistake so that it will cause a shock,” he said in website comments.