Updated

Two Lebanese army officers and a soldier were killed on Sunday in a clash with supporters of a radical Sunni Muslim sheikh opposed to the powerful Shiite movement Hezbollah, an army statement said.

"An armed group loyal to Sheikh Ahmad al-Assir attacked, for no reason, a Lebanese army checkpoint in the village of Abra" on the outskirts of the southern Lebanese city of Sidon, the military said.

"Two officers and a soldier were killed, while several others were wounded. Several military vehicles were damaged," the statement added, updating the army's earlier toll of two dead.

The clash broke out when Assir's supporters surrounded an army checkpoint in Abra, where a vehicle transporting other supporters of the Sunni cleric had been stopped, a security source told AFP earlier.

"After the armed men attacked (the army) with gunfire" the army fired back, the source added.

An AFP journalist reported that explosions were heard two kilometres (more than a mile) away.

The correspondent saw civilians fleeing the fighting, both by car and on foot.

Businesses in Abra closed for the day because of the raging gunfire.

"The shells are raining down on us, and there is intense gunfire," a witness told AFP by telephone.

More troops deployed to the area as the clashes raged through the afternoon.

The controversial Sunni sheikh called on his supporters last week to fire on apartments in Abra that he says house Hezbollah members.

Abra is home to a mosque where Assir leads the main weekly prayers on Fridays. The sheikh believes Hezbollah uses the Abra apartments to keep him under surveillance.

His supporters clashed with Hezbollah in Abra last week in fighting that left one man dead.

Assir was unknown until around two years ago, when he rose to prominence over his radical opposition to Hezbollah and its ally, the Damascus regime of President Bashar al-Assad.

Syria-related tensions have soared in Lebanon, deepening sectarian rifts between Sunnis and Shiites.

Shiite Hezbollah supports Assad's regime, while the Sunni-dominated opposition backs the rebels fighting it.

During Sunday's fighting, Assir distributed a video message via mobile phone addressed to his supporters.

"We are being attacked by the Lebanese army," Assir said, describing the military as "sectarian" and accusing it of supporting Hezbollah chief Hassan Nasrallah.

"I call on everyone... to cut off roads and to all honourable soldiers, Sunni and non-Sunni, to quit the army immediately," Assir said in the message.

He urged supporters across Lebanon to flock to Abra "to help defend our religion, our honour and our women".