The source added that a member of the Lebanese Hezbollah movement was also killed.
Hezbollah fighters lay the ambush early on Saturday, the source said adding that the bodies of the slain al-Nusra Front terrorists were in Hezbollah fighters’ possession.
Another Hezbollah member was wounded in the clashes that followed the ambush.
Fighting erupted between the Hezbollah fighters and al-Qaeda-affiliated al-Nusra Front terrorists in Wadi al-Jamala, on the outskirts of Nahle, a rugged mountainous area along the porous border between Lebanon and Syria.
Earlier, Hezbollah Secretary General Seyyed Hassan Nasrallah says Syria is the pillar of resistance, and the Lebanese resistance movement will stay in the crisis-hit country as long as necessary.
Nasrallah made the remarks in a speech in southern Beirut on Thursday, that marks the occasion of Ashura.
In June, Syrian troops, backed by Hezbollah fighters, fought the foreign-backed militants in Qusayr and regained the strategic town, which borders Lebanon.
RA/NJF