Lebanese security officials say clashes have erupted between unknown gunmen and followers of a radical Sunni cleric in the south of the country.

The officials said automatic rifles and rocket propelled grenades were being used in the fighting that broke out Tuesday afternoon in an eastern suburb of the port city of Sidon.

Sheik Ahmad al-Assir is a critic of the Shiite militant group Hezbollah and has threatened to clear apartments occupied by Hezbollah supporters in the mostly Sunni city. Officials believed the gunmen fighting al-Assir's followers to be Hezbollah sympathizers.

Sectarian tensions have been building in Lebanon since Hezbollah's involvement in the Syrian civil war became public last month

Lebanese army troops deployed in the area of the fighting, the officials said. They spoke anonymously in line with regulations.