Israeli prime minister Benjamin Netanyahu is trying to persuade his cabinet to authorise a military strike against Iran's suspected nuclear weapons programme - a discussion that comes as Israel successfully tests a missile believed capable of carrying a nuclear warhead to Iran, an official said.
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 is due 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 probe of 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 also said Israel's top security chiefs, including the heads of the military and Mossad spy agency, oppose military action.
It is generally understood that such a momentous decision would require a cabinet decision. Israel's 1981 destruction of Iraq's nuclear reactor was preceded by a cabinet vote.
Mr Netanyahu's spokesman Mark Regev refused to comment on the issue but did say there is a "decision-making process which has stood the test of time... There have been precedents, and the process works".
Iran's military chief, General Hasan Firouzabadi, said his country takes Israeli threats seriously and vowed fierce retaliation. "We are fully prepared to use our proper equipment to punish any mistake so that it will cause a shock," he said in comments posted on the website of the Revolutionary Guard, Iran's most powerful military force.