Amid indications that Hezbollah is rearming itself, Israel assassinated a top official of the Lebanese terrorist group in an airstrike on Sunday in Beirut. The strike, which killed Haytham Ali Tabatabai, the group’s chief of staff, was the first such attack in the Lebanese capital in five months and part of a recent escalation in Israeli strikes to blunt Hezbollah’s rebuilding.

Tabatabai served as Hezbollah’s chief of staff for the last year, when a ceasefire agreement was reached between Israel and Lebanon, according to the Israel Defense Forces. Before that, the army said, Tabatabai oversaw Hezbollah’s combat operations against Israel and had held a series of senior positions since he joined the group in the 1980s, including commander of the Radwan Force unit and head of Hezbollah’s operations in Syria. 

“Tabatabai is a mass murderer,” Israeli Prime Minister Benjamin Netanyahu said in a statement on Sunday evening. 

“His hands are soaked in the blood of many Israelis and Americans, and it is not for nothing that the U.S. put a bounty of five million dollars on his head,” Netanyahu said, in reference to a 2016 decision designating Tabatabai as a Specially Designated Global Terrorist.

“Tabatabai served as a senior commander in the Radwan Force. This is the force that prepared to conquer the Galilee and slaughter many of our citizens,” Netanyahu added. “Recently, he led Hezbollah’s renewed efforts to rearm, this is of course after the heavy blows Hezbollah suffered in the ‘Pager Operation,’ in the damage to its missile stockpiles, and of course, in the elimination of [Hezbollah Secretary-General Hassan] Nasrallah,” the prime minister said, stressing that Israel would not allow the group to rebuild and calling on the Lebanese government to “fulfill its commitment to disarm Hezbollah.”

Israel reportedly did not notify the U.S. in advance of the strike.

The strike killed five people and wounded 25 others, according to Lebanon’s Health Ministry.

Lebanese President Joseph Aoun condemned the strike and called on the international community to intervene “to stop the attacks on Lebanon and its people.”

The Israeli army said in its statement that it “will act against efforts to rebuild and rearm the Hezbollah terrorist organization and will operate to remove any threat posed to Israeli civilians,” adding that it “remains committed to the understandings reached between the State of Israel and Lebanon.”

“Hezbollah’s leadership is studying the matter of response and will take the appropriate decision,” Mahmoud Qamati, deputy chair of Hezbollah’s political council, told reporters, according to the Associated Press.

Israeli intelligence officials told Haaretz they believe that Hezbollah may retaliate with attacks on Jewish, Israeli or Israeli-linked targets in foreign countries, rather than directly attacking Israel.