The Lebanese government has told the army to take over security in the restive coastal city of Tripoli for six months, caretaker Prime Minister Najib Mikati said on Monday.
Ten people were killed in weekend clashes between Tripoli's Alawite minority, which supports Syria's Alawite President Bashar al-Assad, and majority Sunni Muslims who back his foes.
Violence in the northern city has killed more than 100 people this year and paralyzed business activity there.
Mikati, a Sunni from Tripoli, told Lebanon's LBC television he had agreed with President Michel Suleiman and armed forces commander General Jean Qahwaji to "put Tripoli under the complete supervision of the army" for six months.
The conflict in Tripoli, 30 km (19 miles) from the Syrian border, reflects the sectarian gulf in Lebanon over Syria's civil war.
Some Lebanese Sunnis are fighting alongside anti-Assad rebels, while Lebanon's Shi'ite Hezbollah militia is credited with helping Assad regain the military initiative.
Sunni-Alawite tensions have festered in Tripoli since Lebanon's 1975-1990 civil war, when Syrian troops then deployed in the country helped Alawites fight their Islamist rivals.