BEIRUT — With rebels fleeing into neighboring Lebanon, Syrian government troops and Hezbollah fighters captured a strategic town near the frontier Sunday, ousting opposition fighters from their last stronghold in the vital border area.

Yabroud was a major smuggling hub for the rebels trying to overthrow President Bashar Assad. The town’s fall is the latest in a string of strategic gains by Assad’s forces that have consolidated authority in the past months in Syria’s major cities, including the capital, Damascus.

Militants from Lebanon’s Shiite group Hezbollah have been instrumental to Assad’s success on the battlefield, and support from the Iranian-backed fighters appears to have tipped the balance into the government’s favor in Yabroud. However, the fact that opposition fighters fled into Lebanon, where Hezbollah is a major force, suggests the conflict could bleed further into Syria’s neighbor. The civil war already has ignited polarizing sectarian tensions between Lebanon’s Sunnis and Shiites.

“It’s a good day for Assad,” said Fawaz A. Gerges, director of the Middle East Center at the London School of Economics. “He has not only survived the past three years, but his army is intact and on a rebound, with his allies Hezbollah firmly behind him.”

However, Gerges warned the fall of Yabroud will reverberate in neighboring Lebanon, “pouring gasoline on sectarian divisions and likely bring more violence” into the country.

Outgunned by Assad’s army and Hezbollah, rebels abandoned their positions on the hills surrounding Yabroud overnight Sunday, collapsing the fighter ranks inside the town and allowing government forces to move in from the east shortly after dawn, both sides reported.