BEIRUT - Hezbollah fighters and gunmen from al-Qaida's Syria wing Nusra Front clashed on Tuesday in eastern Lebanon near the border with Syria, Hezbollah's television channel and a military source in the Lebanese group said.The source said the group ambushed Nusra fighters in "advanced positions" in the outskirts of the mountain towns of Toufeil and Britel. Nusra Front fighters have regularly been active in areas close to the Syrian border and have targeted Hezbollah and Lebanese army positions in the past."The clashes erupted hours ago, their casualties are very high," the Hezbollah source told Reuters. Al-Manar TV said Hezbollah fighters destroyed five military vehicles for Nusra Front and killed at least 12 fighters.There was no immediate reaction from Nusra Front, which has recently been on the offensive in northwestern Syria.A Lebanese security source said the clashes were continuing on the outskirts of Britel and in the Toufeil area and were around 50 km (30 miles) from the Syrian border.The Shi'ite Muslim Hezbollah is a staunch ally of Syria's President Bashar Assad and has sent hundreds of combatants to fight alongside his forces in the four-year civil war. The Sunni Muslim Nusra Front is pushing for the downfall of Assad.