At least 12 children and young people were killed on Saturday when multiple rockets struck a village in the Israeli-controlled Golan Heights, Israeli officials said, in an attack that has sparked fears of a significant escalation in the long-standing conflict.

The IDF responded later on Saturday night by striking Hezbollah facilities, which denies initially attacking.

Targets included weapon depots and other infrastructure in Samricha and Burj el-Shemali near Tyre, the Bekaa Valley, and the areas of Kafr Kila, Raba al-Talatine, Khiam, and Tair Harfa in southern Lebanon.

The Israeli Foreign Ministry stated on Sunday that Hezbollah “crossed all red lines” with the deadly hit on the football field, resulting in the deaths of 12 people, mostly minors.

“The Saturday massacre constitutes a crossing of all red lines by Hezbollah. This is not an army fighting another army but a terrorist organization deliberately targeting civilians,” the ministry said in a statement.

The ministry claimed that “an Iranian missile” caused the death of “our boys and girls.” “Hezbollah is the only terrorist organization that has these rockets in its arsenal,” it said. “Israel will exercise its right and duty to act in self-defense and will respond to the massacre.”

Israeli Prime Minister Benjamin Netanyahu had earlier vowed that Hezbollah would “pay a heavy price.”

Mohammad Afif, a senior Hezbollah official, denied responsibility for the strike that hit Majdal Shams, speaking to Reuters. In a statement, the Iran-backed militant organization said it had “absolutely no connection to the incident,” accusing hostile media of “false claims.” On Sunday, Iran warned Israel against what it called a “new adventure” in Lebanon, according to a statement by Foreign Ministry spokesman Nasser Kanaani.

Fears of a dangerous escalation

The United States, leading diplomatic efforts to de-escalate the conflict at the Lebanon-Israel border (while also equipping Israel), condemned the attack as horrific but did not directly blame Hezbollah.

The White House statement noted that US support for Israel’s security is unwavering and that “they will continue to support efforts to end these horrific attacks along the Blue Line, which must be a top priority.” The Blue Line refers to the border between Lebanon and Israel, monitored by the UN peacekeeping mission known as UNIFIL.

UN Special Coordinator for Lebanon Jeanine Hennis-Plasschaert and UNIFIL force commander Major General Aroldo Lázaro warned that further intensification of attacks “could trigger a broader conflagration that would plunge the entire region into a catastrophe beyond imagination.” They urged maximum restraint from all sides, adding that they are in contact with both Israel and Lebanon.