Israeli leaders are again talking about possible military action against Iran. This is, at best, mischievous and, at worst, irresponsible, especially when diplomacy has time to run.

Iran’s nuclear ambitions are clearly dangerous to the region. Iranian leaders operated a nuclear program in secret for two decades and continued to invest in it even after its discovery in 2002. The government is outspoken in its hatred of Israel. It supports President Bashar al-Assad of Syria and extremist groups like Hezbollah. If Iran gets a weapon, other countries in the region may want one, too.

But while Israel’s defense minster, Ehud Barak, suggested on Israel Radio Thursday that Iran had made significant progress toward acquiring weapons capability — citing what he said was a new American intelligence report — there is no proof that Iran is at the point of producing a weapon. Obama administration officials would not confirm the existence of such a report, and, in any case, continue to insist strongly that Iran is not on the verge of achieving a weapon.

It is impossible to know what Prime Minister Benjamin Netanyahu is planning or why he has ignored American entreaties to give diplomacy a reasonable chance. There is, however, persistent speculation in Israel that Mr. Netanyahu wants to attack in the coming weeks in the belief that President Obama will be forced to support the decision because of his political needs in his re-election campaign. Such a move would be outrageously cynical.

Military action is no quick fix. Even a sustained air campaign would likely set Iran’s nuclear program back only by a few years and would rally tremendous sympathy for Iran both at home and abroad. The current international consensus for sanctions, and the punishments, would evaporate. It would shift international outrage against Mr. Assad’s brutality in Syria to Israel. Many former Israeli intelligence and military officials have spoken out against a military attack. And polls show that many ordinary Israelis oppose unilateral action.

Even so, Mr. Netanyahu’s hard-line government has never liked the idea of negotiating with Iran on the nuclear issue, and, at times, seems in a rush to end them altogether. On Sunday, the deputy foreign minister, Danny Ayalon, told Israel Radio that the United States and the other major powers should simply “declare today that the talks have failed.”

Of course, it is disappointing that the negotiations have made so little progress. No one can be sure that any mix of diplomacy and sanctions will persuade Iran to give up its ambitions. But the talks have been under way only since April, and the toughest sanctions just took effect in July.

There is still time for intensified diplomacy. It would be best served if the major powers stay united and Israeli leaders temper loose talk of war.