At least 16 fighters were killed in clashes between Syrian rebels and Lebanon's Shiite militant group Hezbollah on the Lebanese border over the weekend, a monitoring group said Monday.
"Seven members of Hezbollah were killed and 31 wounded" in the clashes which raged from Saturday until Sunday night, said Rami Abdel Rahman, head of the Syrian Observatory for Human Rights.
He told AFP that the Syrian rebels lost nine fighters and 23 of them were wounded in the battle waged in an undemarcated area of the border between Qalamun in Syria and Lebanon's Arsal.
Hezbollah initiated the showdown in a bid to rid the region of rebel fighters following a string of daily clashes, said Abdel Rahman.
"But they fell into an ambush by rebels ... before Hezbollah reinforcements arrived and the fighting intensified," he said, adding that the Shiite group captured 11 rebels.
On Sunday, a Hezbollah source and a Lebanese security official gave a preliminary toll of three Hezbollah fighters and three Syrian rebels killed.
The long and porous border region is often used by smugglers, refugees and fighters.
Arsal and the area around it are largely Sunni Muslim, and residents sympathise with the Sunni-led uprising against Syrian President Bashar al-Assad.
In April, Syrian forces backed by allied fighters from Hezbollah retook control of most of the Qalamun region.
But Syrian activists say hundreds of opposition fighters have taken refuge in the caves and hills in the border area, using it as a rear base from which to launch attacks inside Syria.
Last month, Lebanese army forces carried out raids in the area targeting militants with ties to "terrorist groups", an army statement said at the time.