Israeli warplanes have struck a target south of the Lebanese capital Beirut.
The attack came a day after militants fired four rockets into northern Israel, the Israeli military and a Palestinian official said.
The Israeli military said that Israeli warplanes targeted "a terror site located between Beirut and Sidon in response" to the rocket attack. It was the first air raid on the area since the 2006 war between Israel and Lebanon's militant Hezbollah group.
Ramez Mustafa, a Lebanon-based official with the Popular Front for the Liberation of Palestine-General Command (PFLP-GC), said the raid occurred at 4am local time, and caused no casualties or material damage. He said the warplanes struck the coastal town of Naameh, 10 miles south of Beirut. The Palestinian group is active in the area and has a base there.
An Associated Press photographer in Naameh said the raid targeted a PFLP-GC base in a valley in the town. Lebanese troops in the area prevented journalists from reaching the base.
An Israeli army statement issued after the air raid said: "Yesterday's attack is a blatant breach of Israeli sovereignty that jeopardised Israeli civilian life. Israel will not tolerate terrorist aggression originating from Lebanese territory."
O Thursday, militants in Lebanon fired four rockets into Israel, setting off air raid sirens and startling a nation already on edge over turmoil along its northern and southern borders.
Lt Col Peter Lerner, a military spokesman, said three rockets landed in northern Israel, while a fourth was intercepted by Israel's "Iron Dome" rocket defence system. No one was injured, and the military dismissed the attack as an "isolated incident".
But the rockets added to the nation's fears at a time it is nervously watching unrest in neighbouring Syria, where the government has been accused of using chemical weapons against rebels and civilians this week. It is also worried about Egypt to the south, where Islamic militants have stepped up their activities near the Israeli border in the wake of a military coup.
The Abdullah Azzam Brigades, an al Qaida-inspired group based in Lebanon, claimed responsibility for the attack in a post on the Twitter account of Sirajuddin Zurayqat, a prominent Islamic militant leader. It said the rockets were capable of flying 25 miles, putting the Israeli city of Haifa in its range. The group, designated a terrorist organisation by the US, has claimed responsibility for past rocket attacks on Israel.