The Israeli strikes targeted the Lebanese areas of Sabrinha, Borj El Chmali, Beka'a, Kfar Kila, Rab a-Taltin, al Khyam and Tir Hafa, according to an Israeli military statement.
"We are greatly increasing our preparedness for the next stage of the fighting in the north," said the head of the Israeli army's general staff, Herzi Halevi, during a visit to the football field hit by rockets launched by the Lebanese Islamist movement Hezbollah.
"When necessary, we will act firmly. Our duty is to restore security to the people of the north in their homes in the Galilee and the Golan Heights. This is our full commitment," he added.
The rocket fired was a Falaq 1, an Iranian missile with a 53-kilogram explosive charge, which is the exclusive property of Hezbollah, Halevi said.
"We will strike hard against the enemy," Israeli Defense Minister Yoav Gallant said in a conversation with the spiritual leader of the Druze community, Sheikh Mowafaq Tarif, who also spoke with Israeli Prime Minister Benjamin Netanyahu, who is in the United States.
The projectile from Hezbollah, a pro-Iran movement, landed on a soccer field in the Druze city of Majdal Shams, where Druze boys and girls (an Arab community) were playing, killing 12 people. The identities of eleven of the victims, all minors between the ages of 10 and 16, have been confirmed.
"This is the deadliest attack on Israeli civilians since October 7," Israeli army spokesman Daniel Hagari said in a statement.
Israeli Prime Minister Benjamin Netanyahu is already traveling back from the United States. Netanyahy is expected to arrive in Israel early this afternoon and intends to immediately convene the security cabinet.
Netanyahu promised on Saturday night that "Hezbollah will pay a heavy price, which it has not paid so far", for the attack on Majdal Shams.
The Lebanese Shiite group Hezbollah, for its part, denied having attacked the city of Majdal Shams, although it claimed responsibility on Saturday for seven attacks in other parts of northern Israel, including the Golan Heights.
However, the army accused Hezbollah of lying and assured that it "knows exactly" the launch point of the "rocket", a city in the Chebaa Farms area, in southern Lebanon, controlled by the Shiite group.
The border between Israel and Lebanon - an ally of the Palestinians - is experiencing its most tense moment since 2006, with intense hostility since the start of the war in the Gaza Strip, on October 7.
The hostilities have already killed around 565 people, most of them in Lebanon and some in Syria, including Hezbollah militants and civilians. In Israel, 46 people have died, 22 military personnel and 24 civilians, according to the Israeli army.
