LABWEH, Lebanon — The Lebanese army sent commandos to the tense border with Syria on Monday, as fears rose that the ongoing flight of rebels from one of their fallen strongholds into a flashpoint region of Lebanon would trigger violence.
Lebanon has been on edge since the Syrian town of Yabroud was taken by President Bashar Assad’s troops on Sunday. Its rebel defenders started pouring into the Lebanese Sunni-dominated town of Arsal, which is surrounded by Shi’ite villages guarded by pro-Assad Hezbollah militants.
Sectarian violence between Lebanon’s Sunnis and Shi’ites linked to Syria’s civil war has killed scores of people in recent months. The presence in the same area of Lebanon of Hezbollah and Sunni rebels — who had been fighting each other in Syria — risks a polarizing new flare-up.
Many Lebanese Shi’ites back Assad’s government, dominated by members of his minority Alawite sect, an offshoot of Shi’ite Islam. Hezbollah has fought alongside Assad’s troops. On the other side, many Lebanese Sunnis back Sunni-dominated rebels.
On Monday, three rockets struck the predominantly Shi’ite towns of Labweh and Nabi Othman near Arsal, wounding at least one person and causing some damage, the army said. The rockets were fired from inside Syria, the army said.
In a separate development Monday, Secretary of State John Kerry named career diplomat and Middle East hand Daniel Rubinstein as the new special envoy for Syria. He replaces Robert Ford, a veteran diplomat who retired earlier this year amid a breakdown in talks between the Syrian government and opposition forces.
Ford, who also served as US ambassador to Syria, retired at the end of February. Like Ford, Rubinstein speaks fluent Arabic and has served in numerous positions at embassies around the Mideast, including in Israel, Jordan, Iraq, Tunisia, and Syria. He will travel to the region in the coming weeks.
Monday’s rocket barrage on the Shi’ite towns near Arsal appears to have sparked sectarian tensions in the area.
Some angry Labweh residents claimed the rockets were fired from Arsal and closed off the main road between the two towns with sand barriers, guarded by dozens of Hezbollah fighters. They later closed other, smaller roads leading to Arsal, isolating the town from the rest of Lebanon.
Hezbollah fighters prevented journalists from entering Arsal. Only Lebanese troops were able to drive on the road.
Syrian rebels and their sympathizers are believed to have considerable power in Arsal. Ramez Amhaz, the mayor of Labweh, called on the residents of Arsal to let Lebanese security forces take charge of the town ‘‘because now you cannot control the Syrians in Arsal.’’
‘‘The people here will not be shelled and be subjected to rockets, then say that [Arsal residents] are our brothers,’’ Amhaz told Lebanon’s Al-Jadeed TV.
Earlier in the day, Lebanese troops and commandos in desert camouflage patrolled the rugged border area on foot. On one patrol, near the northeastern village of Fakiha, they came across an abandoned SUV and fired a rocket-propelled grenade at it, turning the vehicle into a fireball and leaving a four-yard-wide crater on the ground. They could not take the chance of it being a car bomb.
In footage broadcast live on state television in Damascus, Syrian army officers raised the national flag in Yabroud’s main square and covered a rebel flag with banners praising Assad’s troops.
The fall of Yabroud, a smuggling hub for the rebels trying to overthrow Assad, was a major gain for Syrian government troops. It was also the Syrian opposition’s last stronghold in the vital border area. The campaign consolidated the government’s hold on the capital Damascus and the central Syrian city of Homs.
Yabroud’s fall came after months of fighting in the mountainous Qalamoun region between Assad’s forces and Hezbollah fighters on one side and the rebels, mostly Islamist militant groups, on the other.
A Lebanese militant Sunni group claimed responsibility Monday for a car bombing the previous night in Nabi Othman, a predominantly Shi’ite town in Lebanon’s Bekaa Valley that also has a significant Christian community.
The Nusra Front in Lebanon said in a statement posted on its Twitter account that the attack, in which two people were killed and 14 were wounded, was in revenge for Hezbollah’s support for Assad and ‘‘a quick response’’ for the fall of Yabroud into Syrian government hands.