ARSAL, Lebanon — Sunnis and Shiites from Lebanon are streaming into Syria to take up arms on opposite sides of a fierce battle over a rebel stronghold — a fight that has effectively erased the border between the two countries and underlined how Lebanon is being sucked into the civil war next door.
The northeastern Lebanese town of Arsal, dominated by Sunnis, has become a key logistical base for the Syrian rebels who have been fighting for months to keep their hold on the strategic Syrian town of Yabroud, only 20 miles away across the border.
On a recent day, armed fighters in pickup trucks and on motorbikes were seen scrambling down dusty roads out of Arsal into the mountains to cross into Syria and head to Yabroud. Syrian rebels move freely back and forth across the border, and rebels wounded in the battle are brought to Arsal for treatment in clandestine hospitals.
At the same time, Lebanese Shiite fighters from the Hezbollah guerrilla group are crossing into Syria to fight alongside the forces of Syrian President Bashar Assad that have been besieging Yabroud since November.
For the past three years, Lebanon has been struggling with the spillover from Syria's civil war. Sectarian tensions in Lebanon have escalated, as its Sunni community largely supports the mainly Sunni Syrian rebel movement, while its Shiites back Assad. Hezbollah, the most powerful armed force in Lebanon, has thrown its weight behind Assad, sending fighters who have tipped some battles in the government's favor.
The violence has blown back into Lebanon itself, with suspected Sunni extremists carrying out a string of retaliatory bombings against Hezbollah-controlled Shiite areas.
The fighting has contributed to a wave of refugees fleeing across the border to Arsal. In the past two weeks alone, 13,000 arrived in Arsal, which has already been overwhelmed by Syrians settling in makeshift camps in the fields and hills on its outskirts.