Iran also wanted to seize what it viewed as a “golden opportunity” to retaliate at this scale, because Israel was being so widely criticized over Gaza, including by its key allies, like the United States, Mr. Imani said.

Iran’s reach for regional hegemony, enhanced by its proxies and its nuclear abilities, has antagonized the traditional Sunni Arab governments of the region, including Egypt, Saudi Arabia, Jordan and Gulf nations. The Islamic Revolution that overthrew the monarchy in 1979 was at its start aimed at regional revolution, overthrowing these governments, most of which are monarchies or military dictatorships, so Israel’s efforts to limit the power of Iran, a non-Arab Shiite nation, have had quiet support from Arab countries, including Israel’s war against Hamas.

Now the risks of regional escalation have gone up considerably. Iran has been careful during the war in Gaza to restrain its proxies surrounding Israel against major strikes, and to avoid major Israeli retaliation against Hezbollah in southern Lebanon in particular. Hezbollah, with its many thousands of rockets aimed at Israel, is considered a major deterrent preventing Israel from directly attacking Iran and especially its nuclear and missile program.

Given Iran’s new isolation after this attack, Israel should not respond, said Bruno Tertrais, the deputy director of the Foundation for Strategic Research in France. “But a threshold has been crossed,” he said. And the threshold for “a massive Israeli attack on Iranian territory,” he continued, “always an extreme option for Israel whatever the commentators say — is now lowered.”

Mr. Netanyahu, who has been warning of the threat from Iran for two decades and faces severe pressure to respond from within his shaky far-right coalition, may choose to riposte with more force, either at Iran directly or at Hezbollah. But Washington, not having been warned of the Damascus attack, is likely to insist on prior consultation now.