Syrian troops supported by Hezbollah militants launched an offensive to retake a major town near Lebanon from rebels on Sunday (May 19), the heaviest fighting yet involving the Lebanese armed group, opposition activists said.

At least 32 people were killed when rebel fighters clashed with mechanised Syrian army units and Hezbollah guerillas in nine points in and around the town of Qusair, 10 km (six miles) from the border with Lebanon's Bekaa valley, they said.

Speaking from Qusair, activist Hadi Abdallah said Syrian warplanes bombed Qusair in the morning and shells were hitting the town at a rate of up to 50 a minute.

War planes flew overhead on Sunday dropping bombs on an already half-destroyed urban landscape, two video clips uploaded to a social media website purport to show.

The clips show the camera operators trying to track the war planes' movements and the subsequent impact of massive bombs.

Heavy small arms fire is also heard, suggesting that that war planes were coming under intense ground fire.

Activist Abdallah said the Syrian army was hitting Qusair with tanks and artillery from the north and east while Hezbollah was firing mortars and rockets from the south and west.

The region near the Orontos River has been segregated into Sunni and Shi'ite villages in the civil war that grew out of protests against Syrian President Bashar al-Assad.

It is vital for Assad, who belongs to the Alawite sect, an offshoot of Shi'ite Islam, to keep open a route from Shi'ite Hezbollah's strongholds in the Bekaa to areas near Syria's Mediterranean coast inhabited by co-religionist Alawites.

Opposition sources say Syria's coastal region could serve as an Alawite statelet in case Assad falls in Damascus, in a potential fragmentation of Syria along ethnic and sectarian lines that raises the prospect of many more deaths.

Sources in Lebanon's Bekaa Valley said shells fired by rebels hit the edges of the town of Hermel, a stronghold of Hezbollah, which is backed by Iran, but no casualties were reported.

Syrian Television said the army was "leading an operation against terrorists in Qusair", with troops reaching the town's centre.

Presented by Adam Justice