An Israeli soldier has been killed in cross-border gunfire near the Lebanese border, the Israeli military has said.
Gunfire was exchanged near the village of Naqoura, at around 8:30pm on Sunday night.
Sources on both sides say the shooting originated from the Lebanese side of the border, but it remains unclear what the target of the shooting was, after Israel initially claimed a civilian vehicle had been shot at.
"A sniper from Lebanese Armed Forces opened fire at a civilian vehicle travelling on the Israeli side," an Israeli army spokesperson said, without giving details of any casualties.
"We will not tolerate aggression against the state of Israel and maintain the right to exercise self-defence."
There was no immediate confirmation of an armed Israeli response, and it is not yet known what prompted the shooting - despite local media speculation that Israeli troops had crossed the border.
Lebanese sources told Reuters said they had lost contact with the Lebanese soldier after the shooting, which took place at the western tip of the border region, across which Israel and Hezbollah fought a 34-day war in 2006. There was suspicion that the sniper was being held by Israeli troops, reported Israeli daily Haaretz.
The UN peacekeeping force in southern Lebanon said they had been informed about "a serious incident" at the border.
"We are now trying to determine the facts of what happened and the situation is ongoing," UNIFIL spokesman Andrea Tenenti said.
"UNIFIL's force commander is in contact with counterparts in the Lebanese and Israeli army, urging restraint."
Tenenti said that both sides were cooperating with UNIFIL after the incident, which he said appeared to have happened on the Israeli side of the Blue Line which divides Lebanese and Israeli forces.
In August, four Israeli soldiers on patrol were wounded in a blast 400 metres inside Lebanese territory, Lebanon's army and a UN peacekeeper in the border region said.