Arsal has also taken in hundreds of Syrian refugee families, most from villages in Homs province, about 25 kilometers (15 miles) to the northeast. Some of the refugees rent apartments, while others live with Arsal families or in a small camp on the outskirts of town, where tents are being replaced by cinderblock shacks to prepare for the harsh mountain winter.
Rebel fighters have also used Arsal as a temporary haven to rest from the fighting across the border.
Peach farmer-turned-fighter Mohammed Yousef left his village of Zara in Homs province late last month after airstrikes destroyed his home and many others in the village. He reached Arsal after a seven-hour cross-border trek across mountainous terrain, he said, adding that several dozen of his fellow rebels do the same from time to time.
"Arsal is the ... mother of the revolution," the 25-year-old said affectionately of his Lebanese hosts who have sheltered his extended family of 10 in an empty building.
Yousef dismissed Syrian troops as largely ineffective, saying most can be bribed, but swore to exact revenge from Hezbollah, which he blamed for the destruction in his village. "We want to slaughter Hassan Nasrallah, the dog," Yousef said of the Hezbollah leader. "He shelled us, he destroyed our houses, and killed our children."
Hezbollah denies that it is fighting alongside regime forces, and a spokesman declined further comment Monday.
Lebanese security officials have said a number of Hezbollah activists recently buried in the Bekaa Valley had been killed in fighting in Syria, while Susan Rice, the U.S. ambassador to the United Nations, told the U.N. Security Council on Monday that "Nasrallah's fighters are now part of Assad's killing machine."
Hojeiri, the school principal, said tensions between Shiites and Sunnis in the valley have been rising since the start of the Syrian revolt. Each side is aware of the other's loyalties, and people are careful not to talk about politics when someone from the other sect is present, he said.
"People here don't want another (sectarian) war," he said.
In the past, ties between the communities were civil and even warm, he said, noting that some 200 men in Arsal are married to Shiite women from nearby villages.
For years, religious differences seemed unimportant, he said. Even during Lebanon's civil war, with its frequently shifting alliances, Shiites and Sunnis were partners more often than they were foes.
Timor Goksel, a former official in the U.N. peacekeeping force in south Lebanon, said he believes the two sides have too much to lose by bringing the Syrian conflict home.
"Sunnis are very much involved in stone quarrying and the Shiite families are mostly involved in the hashish business," he said. "Both sides respect each other's turfs and have their own livelihoods, hashish and stone."
Perhaps that's why the valley has not seen sectarian clashes — unlike the majority-Sunni Tripoli, where sporadic fighting between pro- and anti-Syrian groups has killed more than two dozen people since May.
However, Sarkis Naoum, a columnist for Lebanon's An Nahar daily said the sectarian tensions bubbling under the surface could erupt at any time.
"If anything major happens, what is happening in Syria could expand into Lebanon," he said.
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