AL QASR, Lebanon -- Masked men in camouflage toting Kalashnikov rifles fan out through a dusty olive grove, part of a group of Hezbollah-backed fighters from Lebanon who are patrolling both sides of a porous border stretch with Syria.
The gunmen on the edge of the border village of al-Qasr say their mission is to protect Shia on the Syrian side who claim their homes, villages and families have come under attack from Sunni rebels.
Hezbollah chief Sheik Hassan Nasrallah, leader of many of Lebanon's Shia and a staunch ally of Syrian President Bashar Assad, has said his group is supporting the cadres of fighters who call themselves Popular Committees.
It is confirmation that the powerful Lebanese militant group is playing a growing role in the civil war just across the border.
Syria's regime is dominated by minority Alawites, an offshoot of Shia Islam, while the rebels opposing Assad are mostly from the Sunni majority. Assad's major allies, Hezbollah and Iran, are both Shia.
The sectarian tensions in the civil war have spilled over to Lebanon, which has a similar ethnic divide and a long history of civil war and domination by Syria. Deadly gun battles have broken out in Lebanon recently between supporters of both sides of the Syrian war.
But more broadly, Hezbollah's deepening involvement shows how the Syrian civil war is exacerbating tensions between Shia and Sunni around the Middle East.
Syrian rebels accuse Hezbollah of fighting alongside Assad's troops and attacking rebels from inside Lebanese territory.
In recent months, fighting has raged in and around towns and villages inhabited by a community of 15,000 Lebanese Shia who have lived for decades on the Syrian side of a frontier that is not clearly demarcated in places and not fully controlled by border authorities. They are mostly Lebanese citizens, though some have dual citizenship or are Syrian.
Before Syria's uprising erupted two years ago, tens of thousands of Lebanese lived in Syria. The Lebanese Shia enclave on the Syrian side of the border is near the central city of Homs and across from Hermel, a predominantly Shia region of northeastern Lebanon.