A top military commander of Hizbullah died in fighting Sunday in Syria, a Lebanese security source said.

"Ali Bazzi, a high-ranking Hizbullah military commander, was killed today in a combat zone," the source said without specifying the location.

Earlier the Syrian Observatory for Human Rights reported that four Hizbullah fighters died Sunday during battles in Nabuk, one of the last rebel-held areas in the Qalamoun region bordering Lebanon.

"There is fierce fighting in Nabuk between government forces, backed by Lebanese Hizbullah fighters, and al-Nusra Front and the Islamic State of Iraq and the Levant," said the watchdog.

A website for Bint Jbeil, Bazzi's hometown in southern Lebanon, also announced the commander's death and posted pictures of him in military garb and holding an automatic rifle.

"Ali Hussein Bazzi... died a martyr as he was carrying out his sacred duty as a jihadist," read the announcement.

Meanwhile residents of southern Lebanon said that two other Hizbullah fighters -- Ali Saleh and Qassem Ghamloosh -- were also killed in Syria on Sunday and buried.

Hizbullah chief Sayyed Hassan Nasrallah has repeatedly defended his group's involvement in Syria.

On Tuesday he said in an interview with OTV that Hizbullah is fighting in Syria to protect Lebanon from the Syrian rebels, who include jihadists linked to al-Qaida.

Hours after that interview Hizbullah announced the death of one of its top military commanders, Hassan al-Laqqis, saying he was shot dead near Beirut and blaming Israel for his murder.

And on November 28, the southern town of Rishknaniyeh held a funeral for Wissam Sharafeddine, another prominent Hizbullah field commander in Damascus' countryside.

Syrian regime forces made gains Sunday in the key town of Nabuk, according to the Syrian Observatory for Human Rights. Regime forces have surrounded and pounded Nabuk for the past two weeks.

Taking the Nabuk area would cement regime control of territory linking Damascus province with Homs province in central Syria.

Also on Sunday, Hizbullah's al-Manar television broadcast a video showing four booby-trapped vehicles, saying they were seized by the Syrian army in Nabuk and they that were destined to be used in bomb attacks in Lebanon.

“Most of the booby-trapped cars that were sent to Lebanon came from Yabrud and Nabuk via Arsal,” Nasrallah said on Tuesday, noting that had Hizbullah refrained from intervening militarily in Syria's Qusayr and Qalamoun areas, “dozens and hundreds of explosive-rigged cars would have entered Lebanon.”