Fire exchanges reported Saturday night between Lebanese soldiers and Islamists who were demonstrating in Tripoli, northern Lebanon, demanding the release of one of their "terrorist" suspects.
No casualties had been reported immediately.
The protesters, supporters of the revolt against the regime of Syrian President Bashar al-Assad, have tried to approach an office of the Syrian Social Nationalist Party, a pro-Assad Lebanese party, when the shooting took place.
The shootings have targeted a patrol of the Army's Intelligence Service in Bab el-Tebbeneh, according to several media sources.
At least 100 people had previously tried to camp at the southern entrance of Tripoli, the largest city in northern Lebanon.
The authorities said Shadi Mawlawi was arrested as part of an "investigation into his ties to a terrorist organization," without elaborating.
The Syrian authorities have repeatedly said that weapons and fighters passed from Lebanon to help the rebels seeking to topple the Assad regime.