Several people were killed in shelling across the Lebanese-Israeli border, security sources and the Israeli army said.
At least seven people were killed in an Israeli airstrike in the Lebanese border town of Habariyeh.
The killed were linked to the Lebanese Sunni Muslim group al-Jamaa al-Islamiya, which has close links to the pro-Iranian Hezbollah movement.
The Lebanese state-run news agency NNA said "enemy fighter jets had hit a medical centre" belonging to the Islamic group during the night.
It added that the strike killed seven medical staff and wounded four civilians.
The Israeli army confirmed it had attacked a military site in southern Lebanon.
"A major terrorist from the organization 'al-Jamaa al-Islamiya,' who carried out attacks on Israeli territory, was eliminated at the site," it said, adding that his companions were killed.
The Sunni organization from Lebanon had previously announced that it would support the Shiite Hezbollah militia's fight against Israel. The small group is linked to the Muslim Brotherhood.
Hezbollah announced in retaliation that its fighters fired dozens of rockets at the Israeli border town of Kiryat Shmona on Wednesday morning.
According to the Israeli rescue service Magen David Adom, a 25-year-old man was killed when a rocket hit a building in the town where he worked.
Hezbollah said in a statement that the killing of the seven "will not go unpunished."
Since the beginning of the Gaza war after the massacre by the Palestinian Islamist Hamas movement in Israel on October 7, there have been repeated confrontations between Israel's army and militant groups such as Hezbollah in the Israeli-Lebanese border region.
The Iranian-backed militia, which also has close ties to Hamas, has reported more than 240 fighters killed since the Gaza war broke out.
Civilians have also been killed in both countries as a result of mutual shelling. Tens of thousands of residents have also left their home towns on both sides of the border. It is the worst escalation since the second Lebanon war in 2006.
