The Israeli air force struck a Palestinian group in Lebanon Friday, officials said, hours after a different organisation said it had fired four rockets at the Jewish state from Lebanon.
The raid, which the Lebanese army said caused no casualties or damage, nonetheless drew condemnation from the Lebanese government as a violation of its sovereignty after it had vowed to hunt down the perpetrators of Thursday's rocket fire.
UN chief Ban Ki-moon urged all sides to exercise "maximum restraint" and to cooperate with UN peacekeepers in Lebanon to prevent an escalation.
Israeli aircraft "targeted a terror site located between Beirut and Sidon in response to a barrage of four rockets launched at northern Israel yesterday (Thursday)," the military said.
"The pilots reported direct hits to the target."
Palestinian and Lebanese officials said the target was a position of the Popular Front for the Liberation of Palestine - General Command (PFLP-GC), a hardline but secular militant group that said it had nothing to do with Thursday's rocket fire.
The salvo of four rockets, which caused damage but no casualties, was claimed by the Abdullah Azzam Brigades -- an Al-Qaeda-linked Palestinian militant group behind similar rocket fire on Israel in 2009 and 2011.
Army spokesman Brigadier General Yoav Mordechai said the rockets were "launched by the global jihad terror organisation" -- an apparent reference to Al-Qaeda.
Prime Minister Benjamin Netanyahu threatened retaliation, saying on Thursday that "anyone who harms us, or tries to harm us, should know -- we will strike them."
The UN peacekeeping force UNIFIL said it had been in touch with Israeli commanders to press them to halt offensive operations and with Lebanese commanders to urge restraint.
Mission head General Paolo Serra said he told the Israel army "to cease from any offensive military operation" and urged the Lebanese military "to exercise maximum restraint to avoid undesired consequences."
A statement by the UN chief said he was "greatly concerned" by the firing of rockets at Israel.
The UN "is committed to continuing to work with the parties to ensure that the calm that has prevailed continues to be sustained," the statement added.
Two of the four rockets fired on Thursday hit populated areas of northern Israel, causing no casualties but damage.
A third rocket was intercepted by Israel's Iron Dome defence system, the army said. The fourth apparently struck outside Israel.
Israeli media said that armed forces chief Lieutenant General Benny Gantz spoke by phone with his US counterpart, General Martin Dempsey, about the rocket attack and Israel's response, but the reports gave no further details.
Thursday's attack was the first of its kind since November 2011, when the Abdullah Azzam Brigades fired rockets from southern Lebanon at Israel, triggering retaliation by the Israeli military.
The PFLP-GC base targeted was in the Naameh valley south of Beirut. The Palestinian group has a number of heavily fortified positions in Lebanon.
"Around 4 am (0100 GMT), the Israeli air force fired a missile on the Naameh valley without causing any casualties or damage," PFLP-GC spokesman Ramez Mustapha said.
He denied any link between his group and the rockets fired at Israel on Thursday.
Headed by Ahmed Jibril, the PFLP-GC is known for close ties with the Syrian regime of President Bashar al-Assad.
The Lebanese army said: "An Israeli enemy aircraft fired a missile from over the sea towards Naameh where a Palestinian group has a base in underground tunnels."
The strike created a "crater five metres (16 feet) across but caused no casualties or damage."
Lebanese President Michel Sleiman condemned Thursday's rocket fire and denounced the Israeli retaliation, and asked Foreign Minister Adnane Mansour to lodge a complaint with the UN Security Council.
"Border violations are a matter settled by the UNIFIL panel of inquiry and not by aggression and violation of Lebanese sovereignty as Israel did in Naameh," his office said.
Defence Minister Moshe Yaalon said Israel holds Lebanon responsible for what happens on its territory.