Hezbollah flag
Hezbollah flagIsrael news photo: Flash 90

A top military commander of Hezbollah, which is helping Syrian troops battle rebels, has died in fighting in Syria, a Lebanese security source said.

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

Sources have confirmed the death of Bazzi to Al Jazeera.

The Syrian Observatory for Human Rights reported earlier that Hezbollah 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 Hezbollah fighters, and Al-Nusra Front and the Islamic State of Iraq and the Levant," the watchdog said.

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.