Five people have been killed and about 20 injured in sectarian clashes in northern Lebanon linked to unrest in neighbouring Syria, officials say.
The fighting in the city of Tripoli was between Alawite supporters of Syrian President Bashar al-Assad and Sunnis, who back the Syrian opposition.
The violence erupted over the weekend after Sunni cleric Shadi al-Moulawi was arrested on terrorism charges.
His supporters say he was held because of his help to Syrian refugees.
The BBC's Jonathan Head in Istanbul says that community leaders in Lebanon have repeatedly warned of the possibility that the violence in Syria would spill over the border.
Heavy gunfire was heard on Monday in Tripoli's two adjacent districts: the predominantly Sunni Bab al-Tabbaneh and Jabal Mohsen, populated mainly by Alawites.
Syrian President Bashar Al-Assad is a member of the Alawite sect, an offshoot of Shia Islam.
The fighting continued despite several attempts by senior political and religious figures to put an end to it.
Lebanese army units are deployed in the city, but have not been able to enter all of the affected areas.
"The army does not want to intervene without political cover," Tripoli lawmaker Mouin Mereebi told AFP news agency.
The clashes erupted last Saturday after Shadi al-Moulawi was detained on charges of helping a "terrorist group".
Mr Al-Moulawi is an activist who supports the Syrian opposition. Media reports in Lebanon says he entered Syria recently.
Tripoli has recently become home to thousand of Syrian refugees fleeing the violence in Syria.
In February, at least two people were killed in Tripoli as supporters and opponents of Mr Assad clashed.