Saturday. He was defending Sayyida Zeinab," which houses a Shia shrine

southeast of Damascus, "when his group was attacked and he was killed," one resident told AFP, without giving a date.

Hezbollah is a key Damascus backer and has sent fighters into Syria to

support President Bashar al-Assad in his regime's bid to crush a 29-month rebellion.

Fighters of Hezbollah played a key role in the government's recapture in

June of the rebel bastion of Qusayr, near the Lebanese border.

The report of Nisr's killing comes after Hezbollah chief Hassan Nasrallah said he was ready to go to Syria to fight extremists he accused of staging a deadly car bomb attack last Thursday in the southern suburbs of Beirut, a bastion of his movement.

According to a final count, 27 people were killed in the attack.

"I will go myself to Syria if it is so necessary in the battle against the takfiris (radical Sunni Muslims), Hezbollah and I will go to Syria" to fight rebels trying to oust the Damascus regime, Nasrallah said in an angry reaction to the car bombing.

Tensions have soared in fragile Lebanon over the conflict in neighbouring Syria. Though Lebanon is officially neutral, the country is deeply divided between those backing Assad's regime and those who oppose it.