Tensions prevailed in the southern Lebanese city of Sidon on Monday, a day after three people were killed and seven injured in clashes between followers of a Sunni Muslim cleric and supporters of the militant Shiite movement Hezbollah, dpa reported.
Streets were deserted and schools across the port city closed, as the Lebanese army was deployed to the area.
"Army troops have received clear orders from their command to open fire on any gunman," Interior Minister Marwan Charbel said.
The clashes occurred in the Tameer area, on the outskirts of Sidon, when followers of Sheikh Ahmed al-Aseer began removing banners hung by Hezbollah to mark Ashoura, a 10-day Shiite religious ceremony.
"It will be over my dead body if Hezbollah is allowed to erect one banner from now on in our area. We will not keep silent on the blood that was shed on Sunday," al-Aseer was quoted in the local media as saying.
Al-Assir has repeatedly criticized Hezbollah for backing the regime of Syrian President Bashar al-Assad. Many Sunnis in Lebanon back the Sunni-led rebellion against al-Assad.
The violence in neighbouring Syria has in recent months spilled several times into Lebanon, with opponents and supporters of al-Assad clashing in the northern city of Tripoli.