Two people, including a military commander from Lebanon's Alawite minority, have been killed in the city of Tripoli, security sources said, a day after a twin suicide bombing hit the southern suburbs of the capital Beirut, killing six people.
The sources said the Alawite commander, Abdel Rahman Youssef, was shot dead on Thursday as he drove through Tripoli, Lebanon's second largest city, the Reuters news agency reported.
Long-standing tensions between Alawites - a sect derived from Shia Islam - and Sunni Muslims in the Mediterrannean city have been exacerbated by the increasingly sectarian war in neighbouring Syria, leading to frequent bouts of armed conflict.
Syria's President Bashar al-Assad is an Alawite and the rebels fighting to topple him are overwhelmingly Sunni.
A senior official in the pro-Syrian Arab Democratic Party said hooded gunmen on a motorbike carried out the killing in a Sunni neighbourhood, shooting Youssef in the head and stomach.
A party official confirmed the killing and said the commander was in charge of "military" affairs.
Tripoli has been the scene of frequent deadly clashes between Alawite residents of the Jabal Mohsen district, and Sunni Muslims in neighbouring Bab al-Tebbaneh who support the Syrian rebels.
As news of the assassination spread, shots rang out between the two neighbourhoods and at least five people were wounded, with Lebanese army troops moving to seal off the area, the AFP news agency reported.
Lebanon itself is bitterly divided over the war in its larger neighbour, with the Iranian-backed Shia movement Hezbollah having sent fighters to bolster Assad's troops.
On Wednesday, two suicide car bombs exploded near an Iranian cultural centre in Beirut, killing six people.
The attack was claimed by a jihadist group that said it was targeting Hezbollah and Iran, a key ally of the Assad regime.
The bombings and the violence in Tripoli highlight the challenges confronting Lebanon's new government, formed at the weekend after a 10-month political vacuum.