BEIRUT — Fears of a widening conflict in the Middle East are growing as the Hezbollah terrorist organization in Lebanon fired today dozens of rockets at northern Israel — despite American efforts to limit the scope of the conflict.

The Iran-backed Hezbollah warned that the barrage was its initial response to the targeted killing, which is being widely attributed to Israel, of a top leader from the allied terrorist Hamas group at Lebanon’s capital earlier this week. 

The cross-border escalation comes as Secretary Blinken kicks off in Turkey an urgent Middle East diplomatic tour, his fourth to the region since the Israel-Hamas war erupted three months ago. Mr. Blinken met with President Erdogan and the foreign minister, Hakan Fidan, to discuss what Turkey and others can do to exert influence, particularly on Iran and its proxies, to ease tensions, speed up aid deliveries to Gaza, and begin in earnest to plan for reconstruction and governance of postwar Gaza.

At Istanbul, American officials said Mr. Blinken would be seeking Turkish buy-in, or at least consideration, of potential monetary or in-kind contributions to reconstruction efforts and some form of participation in a proposed multi-national force that could operate in or adjacent to the territory. Turkey, and Mr. Erdogan in particular, have been harshly critical of Israel and Prime Minister Netanyahu for the prosecution of the war and its impact on Palestinian civilians.

The immediate difficulty of Mr. Blinken’s task was underscored by the Hezbollah rocket barrage against the Jewish state. The attack came a day after Hezbollah leader, Sayyed Hassan Nasrallah, claimed that his group must retaliate for the killing of the deputy political leader of Hamas,  Saleh Arouri, at a Hezbollah stronghold south of Beirut. 

Mr. Nasrallah said that if Hezbollah did not strike back, all of Lebanon would be vulnerable to Israeli attack. He appeared to be making his case for a response to the Lebanese public, even at the risk of escalating the fighting between Hezbollah and Israel as the war between Israel and Hamas rages on.

Hezbollah said Saturday that it launched 62 rockets toward an Israeli air surveillance base on Mount Meron and that it scored direct hits. The group said rockets also struck two army posts near the border. The Israeli military said about 40 rockets were fired toward Meron and that a base was targeted, but made no mention of the base being hit. It said it struck the Hezbollah cell that fired the rockets.

In recent weeks, Israel has been scaling back its military assault in the north of Gaza and pressing its offensive in the south, vowing to crush Hamas. Israel holds Hamas responsible for civilian casualties, saying the group has embedded within Gaza’s civilian infrastructure. America has urged Israel to do more to prevent harm to civilians, while continuing to send weapons and munitions and shielding its close ally against international censure.

From Turkey, Mr. Blinken will travel to its rival Greece, also a member of the North Atlantic Treaty, and meet Prime Minister Mitsotakis at his residence on the Mediterranean island of Crete. Mr. Mitsotakis and his government have been supportive of American efforts to prevent the Israel-Hamas war from spreading  and have signaled their willingness to assist should the situation deteriorate.

Other stops on Mr. Blinken’s trip include Jordan, followed by Qatar, the United Arab Emirates, and Saudi Arabia. Mr. Blinken is due to visit Israel and the West Bank next week before wrapping up the trip in Egypt.