Israel’s military said that four soldiers were killed and seven others severely wounded in a Hezbollah drone strike on an army base Sunday. The militant group later claimed responsibility for the attack on the base in Binyamina, a town in the north of Israel, saying it was retaliation for a series of Israeli strikes on Beirut earlier in the week that killed 22 people and injured more than 100, according to the Associated Press. Israeli rescue authorities said a total of 61 people were wounded, and that the injured had been transported to hospitals for treatment. It was not immediately clear whether the strike represented a failure of Israel’s advanced air-defense systems. “We are studying and investigating the incident — how a drone infiltrated without warning and struck the base,” said Rear Adm. Daniel Hagari, an Israeli military spokesman, according to The New York Times. “We must provide better defense.” Earlier on Sunday, the U.S. announced that it would send 100 American troops and a Terminal High-Altitude Area Defense (THAAD) anti-missile system to Israel, a sign of the U.S. stepping up its involvement in a deeply polarizing foreign conflict less than three weeks away from the presidential election.