BEIRUT (Reuters) -- At least 16 insurgents from al Qaeda's Syrian wing, the Nusra Front, were killed in clashes with Shiite group Hezbollah in eastern Lebanon on Sunday after launching a major offensive, a source close to Hezbollah said.

Hundreds of the Sunni Muslim insurgents attacked at least 10 Hezbollah bases along a mountainous range close to the Syrian border, and killed two Hezbollah fighters, in the latest spillover of violence from the civil war next door.

"There are at least 16 dead from Nusra Front," the source said, adding that Hezbollah reinforcements from the eastern Bekaa region of Lebanon had joined in the battles.

Hezbollah had issued a call on Sunday to its fighters to defend the area, the source close to Hezbollah and other security officials said. Hezbollah's al-Manar television reported late on Sunday that the group had pushed back the insurgents over the border and the clashes had ended.

Earlier officials put the death toll at eight and said it was expected to rise. They said fighters from Islamic State, another insurgent group based in Syria, were also involved in the clashes but the source close to Hezbollah said only Nusra Front appeared to have taken part.

Armed with mortars and rocket-propelled grenades, the insurgents attacked a large area of territory stretching from south of the town of Baalbek up to areas close to the border town of Arsal. The Lebanese army stayed out of the clashes but has also battled insurgents in the area.

The Sunni insurgents see Iran-backed Hezbollah among their chief foes. Fighters from the Lebanese group have been aiding President Bashar al-Assad in the Syrian civil war, battling Islamist groups such as Nusra Front and Islamic State which has seized tracts of land in Syria and Iraq.

Violence from Syria has often spread into Arsal and surrounding areas, which are also hosting tens of thousands of Syrian refugees.

In August Islamic State and Nusra Front fighters stormed Arsal in the worst spillover of Syria's war into its neighbor to date, killing and capturing members of the Lebanese military. They have since killed at least three of the captive soldiers and are holding an unknown number of others.