The Syrian army, backed by Hezbollah fighters, closed in on the rebel-held city of Zabadani near the border with Lebanon on Friday, a Lebanese security source said.
Violence from Syria's four-year war has regularly tipped over into Lebanon, and militiamen from the Iranian-backed Lebanese Shi'ite Muslim group Hezbollah have been fighting on the side of Syrian President Bashar al-Assad.
The Lebanese television station al-Manar, run by Hezbollah, broadcast footage of fighters in a mountainous area using heavy weapons around Zabadani, and showed the body of at least one enemy combatant.