Security forces battled Islamic militants with automatic rifles and hand grenades in a residential neighborhood of the northern city of Tripoli early Sunday and early reports said there were casualties.
The clashes erupted just before dawn in Tripoli, Lebanon's second-largest city, when a police unit was raiding an apartment occupied by militants, apparently to make arrests.
The armed militants resisted arrest and a gunbattle ensued. It spread to surrounding streets.
Casualties were reported, according to witnesses and to the New TV station in Beirut. Police had no immediate casualty figure.
At about the same time, Palestinian Islamic militants affiliated with al-Qaida took up positions in the refugee camp of Nahr el-Bared as a precautionary measure.
The identity of the militants in Tripoli could not be immediately determined. Tripoli, a predominantly Sunni Muslim city, is known to have Islamic fundamentalists.