An Israeli airstrike killed four people in Beirut early Tuesday, the Lebanese health ministry said, rocking an already shaky ceasefire between Israel and Hezbollah.

The operation marks the latest threat to a fragile four-month truce during which both Israel and Hezbollah have accused each other of violating terms, and came the day after United Nations officials demanded “answers and justice” over the discovery of the bodies of 15 aid workers found in a mass grave in Gaza.

In a joint statement, the Israel Defense Forces, the Shin Bet — Israel’s internal security agency — and its Mossad intelligence agency, said the strike on the southern Beirut suburb and Hezbollah stronghold of Dahiyeh had killed Hassan Ali Badir, who it said was a Hezbollah militant and member of Iran’s Islamic Revolutionary Guard Corps who had recently assisted Hamas.

While Hezbollah did not confirm whether Badir had been killled, Ibrahim Al-Moussawi, one of the group’s members of Lebanon’s parliament, condemned the operation that left seven people injured and said it violated international laws.

“What happened was a major aggression that took the situation to a completely new phase,” Al-Moussawi told NBC News. “We hold the international community and the United States responsible for this crime.”

Lebanon’s President Joseph Aoun also criticized the bombardment, saying in a post on X Tuesday that Israel’s growing aggression in Lebanon had prompted the country to seek support from its international allies.

Israel did not issue any evacuation warnings for the area ahead of the strike, while the U.S. State Department said in a statement Tuesday that hostilities had resumed “because terrorists launched rockets into Israel from Lebanon,” Reuters reported.