In another escalation, a Syrian government helicopter on Wednesday fired three missiles on a border town in Lebanon, lightly wounding one person. At least one of the missiles struck the center of Arsal, according to Lebanese security officials and residents.
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The Arsal attack is the latest incident of Lebanon being pulled into the war next door. Scores of rebels and civilians who fled from the Syrian western town of Qusair last week in the last days of a government military offensive there have taken refuge in Arsal.
The town is predominantly Sunni Muslim, and support for the Syrian rebels fighting to topple President Bashar Assad runs high.
Milhem Hojeiri, a resident, said shrapnel from one of the missiles lightly wounded a schoolteacher in Arsal. He said the town's population has almost doubled in the past two years because of refugees and rebels from Syria who have taken shelter there.
"There is a lot of fear here, the town is fast becoming a casualty of the war in Syria," he said.
The Lebanese officials, who spoke on condition of anonymity in line with regulations, did not provide more details on the Arsal attack.
Meanwhile, the Britain-based Syrian Observatory for Human Rights said at least 60 people, mostly Shiite fighters but also ordinary villagers, were killed on Tuesday in the Syrian village of Hatla in the oil-rich province of Deir el-Zour that borders Iraq.
It was the latest high casualty incident in Syria's conflict, which has killed more than 80,000 people so far, according to the UN.
Thousands of rebels took part in the attack and at least 10 of them were killed in the fighting, said the Observatory.
In Damascus, a government official said the rebels "carried out a massacre against villagers in which older people and children were killed." The official spoke on condition of anonymity because he was not authorized to speak to the media.
The fighting in Deir el-Zour came a week after Syrian troops, backed by Lebanon's militant Shiite Hezbollah group, captured the strategic town of Qusair near the Lebanese border after nearly three weeks of fierce battles that killed dozens of troops, rebels and Hezbollah members.
Hezbollah's involvement in the Qusair battle underlined the group's commitment in support of Assad's regime and edged the civil war in Syria closer to a regional sectarian conflict pitting the Middle East's Iranian-backed Shiite axis against Sunnis.
Most of the armed rebels in Syria are from the country's Sunni majority, while Assad has retained core support among the minorities, including his own Alawite sect, an offshoot of Shiite Islam, along with Christians and Shiites.
An activist based in Deir el-Zour said the rebel attack was in retaliation for an attack Monday by Shiites from Hatla that killed four rebels.
Thaer al-Deiry, who identified himself only by his nickname for fear of government retaliation, said via Skype that rebels gathered and launched a counter attack Tuesday. He said some 150 Shiites from the village fled across the Euphrates River to the government-held village of Jafra.
"The situation in the village is quiet and the Free Syrian Army is in full control," al-Deiry said, referring to the rebels. He added that the village has been under opposition control for more than a year but some of its Shiite residents recently started collecting arms apparently to fight along government troops.
Also Wednesday, the Observatory reported heavy clashes in the central city of Homs, mostly in the neighborhood of Wadi Sayeh. The fighting appeared to be an attempt by government forces to separate two main rebel-held areas in the city, Khaldiyeh and the center of Homs.
Building on its victory in Qusair, the Syrian military has shifted its attention to try to clear rebel-held areas in Homs, a linchpin area linking Damascus with regime strongholds on the Mediterranean coast, and the northern city of Aleppo.
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