Israeli forces killed a senior Hezbollah commander on Wednesday in a drone strike in southern Lebanon, prompting the Lebanese militia to retaliate with a heavy rocket barrage across the border.

The flare-up came as Western diplomats worked to avoid a full-scale war between Israel and Hezbollah, a danger that appears to have grown in recent weeks. Cross-border exchanges of fire have intensified, and Israeli officials have publicly spoken of shifting their military focus from Hamas in the Gaza Strip to Hezbollah, a far more advanced and potent threat.

Amos Hochstein, a senior White House adviser who has become the de facto U.S. envoy in tamping down the Israel-Hezbollah conflict, conferred on Wednesday with French officials in Paris to discuss how to defuse the rising tensions. Jean-Yves Le Drian, President Emmanuel Macron’s special envoy to Lebanon, was among the people with whom he met, according to a person close to the talks, who spoke on the condition of anonymity to discuss sensitive diplomacy.

The Israeli military said its drone strike had killed Mohammad Naameh Nasser, also known as Abu Naameh, who was among the highest-ranking Hezbollah fighters to die in nearly nine months of conflict, according to a senior Lebanese intelligence official, who requested anonymity to discuss the sensitive issue. He said Mr. Nasser had led Hezbollah’s Aziz unit, one of the group’s main fighting forces along the Lebanese border.

Hezbollah confirmed his death, and though it did not explicitly say how he had died, the group said it had fired 100 rockets at military targets over the border as part of an “initial response,” setting off sirens in communities across northern Israel. The Israeli military said that most of that barrage had fallen in open areas, but Hezbollah continued to claim retaliatory attacks into the evening.