Seven people have been killed and more than 70 wounded after fighting in northern Lebanon between two Muslim communities divided over Syria.
Street battles between Sunnis and Alawites in the city of Tripoli continued for a second night running.
Old rivalry between the two groups has been fuelled by conflicting loyalties in the conflict across the border.
Syrian President Bashar al-Assad, an Alawite, is battling largely Sunni opposition fighters.
Lebanese Prime Minister Najib Mikati, himself a Sunni, appealed to both sides to end the "absurd battle" rocking Tripoli, a city of nearly 200,000 people and the country's second-largest.
"We have repeatedly warned against being drawn into this blaze that has spread around Lebanon," he said, speaking of the violence in Syria.
He urged Tripoli residents "not to allow anyone to transform you into ammunition for someone else's war".
Gunmen in the Sunni district of Bab al-Tabbana and Alawites in Jabal Muhsin exchanged gun and grenade fire overnight, residents were quoted as saying by Reuters news agency.
Two men killed were identified as residents of Jabal Muhsin, which overlooks a predominantly Sunni area where five people died, medical sources told the agency.
Tripoli is one of Lebanon's most volatile sectarian faultlines, with a small Alawite community living in the midst of a Sunni majority, the BBC's Barbara Plett reports from the capital, Beirut.
Violence flared several times recently but locals say the last two days of clashes have been particularly intense, our correspondent says.
One witness said heavier weapons were being used, and over a larger area than normal.
Government policy has been to try to disassociate the country from the Syrian crisis, amid concern that it might re-ignite the divisions that fuelled Lebanon's own 15-year civil war, our correspondent adds.
But the more sectarian the violence becomes in Syria, the harder it is to prevent it from seeping across the border, she says.