The leader of the Lebanese militant group Hezbollah, Hassan Nasrallah, said on Thursday that its conflict with Israel had entered a new phase after an Israeli strike in Lebanon’s capital, Beirut, this week. But his vow to respond fell far short of the fiery pledge to escalate that some residents and officials had feared.

Mr. Nasrallah’s speech had been nervously awaited since the Israeli strike on Tuesday, which killed Fuad Shukr, one of his close confidantes and a top-ranking Hezbollah commander. A top Hamas leader was killed in Iran hours later, fueling worries around the Middle East that Israel’s hostilities with Iran and its allies could erupt into all-out regional war.

But although Mr. Nasrallah promised that Hezbollah would respond, he equivocated on the scope and nature of that retaliation.

“We have entered a new phase,” he said, speaking in a televised address during the funeral for Mr. Shukr. “You do not realize the red lines you have crossed,” warned Mr. Nasrallah, addressing Israel directly.

“The response will come, whether spread out or simultaneously,” he added.

Officials and diplomats across the Middle East had been looking to the speech for any indication of whether Hezbollah would alter course in its long-running conflict with Israel, either by escalating its military response or seeking to lower the pressure and avoid all-out war. The speech by Mr. Nasrallah on Thursday appeared to straddle that line.

Although he said the group and its allies were working on “a true response, not a show response as some are trying to suggest,” he added that Israel’s reaction would determine whether the war escalates.