BEIRUT (AP) -- Al-Qaida's Syrian affiliate released a video Saturday showing Lebanese policemen and a soldier captured by the group earlier this month during the most serious cross-border attack since Syria's conflict began more than three years ago.
The captives said they will be killed if Lebanon's militant Hezbollah movement, which backs Syrian President Bashar Assad, does not withdraw its fighters from Syria.
The al-Qaida-branch known as Nusra Front is also demanding the release of detainees held in Lebanon, some of whom were charged in connection to bombings that killed and wounded dozens of people over the past year, according to Lebanese media.
Lebanon's Association of Muslim Scholars, a group of Sunni clerics, has been trying to mediate a deal to release the captives.
The video showed nine bearded men, eight of them in police uniforms and one wearing military fatigues.
Lebanese army commander Jean Kahwaji told An-Nahar newspaper that 20 soldiers remain missing. He defended his command decisions from criticism by local media, saying the soldiers' posts in border areas had been reinforced before the attack.
Other soldiers and policemen are believed to be held by other rebel groups who took part in the Aug. 2 attack on the Lebanese border town of Arsal, which is home to tens of thousands of Syrian refugees.
The video, released by Nusra Front's media arm, al-Manara al-Baydha, appeared genuine and corresponded to other AP reporting of the events.
Syria's civil war has spilled over into Lebanon on multiple occasions and inflamed sectarian tensions in the tiny, multi-confessional country. Lebanese Sunnis tend to support the Sunni rebels while Shiites mainly back Assad.
Hezbollah, which openly joined the war in Syria last year, is not likely to respond to the pleas of the captured troops, who appear to be speaking under duress. Hezbollah leader Hassan Nasrallah has vowed to keep his fighters in Syria as long as needed, portraying the war as a struggle against Sunni extremists who pose a threat to Lebanon as well.
The Hezbollah fighters have been instrumental to Assad's success on the battlefield, and support from the Iranian-backed group appears to have tipped the balance in the government's favor -- especially in areas along the Lebanese border and near the Syrian capital of Damascus.
Meanwhile in Syria, attacks by Muslim extremists against an army air base in the country's north failed to break through fortifications, activists and state media said. They added that the Islamic State group lost "many" fighters in the battle around Tabqa air base that began on Wednesday, although they did not give specific numbers.
Syrian state TV aired a report from the Tabqa air base, the last government-held post in the province of Raqqa, showing the army in control and the bodies of several dead men believed to be Islamic State fighters spread out in an open area. Syrian warplanes were shown taking off from the base to attack Islamic State positions.
"We killed large numbers of them," an officer told the TV, vowing to regain all parts of Raqqa. "We will only rest when we liberate all parts of Raqqa."
The Britain-based Syrian Observatory for Human Rights said the army crushed the latest offensive on the base that began Friday night with a suicide truck bomb. The Observatory's chief, Rami Abdurrahman, said that since the attacks on the base began early Wednesday, nearly 100 Islamic State fighters were killed and over 350 wounded.
Abdurrahman said government forces were flying more troops into the base, while the Islamic State was bringing reinforcements from nearby Syrian regions as well as Iraq, where they control large swaths of territory.
The group said Syrian warplanes attacked a hospital in the nearby town of Tabqa, killing at least three staffers including a doctor. The Raqqa Media Center, an activist collective, also reported the air raid on the hospital, saying a doctor was killed.
The U.N. says more than 191,000 people have been killed since Syria's crisis began in March 2011.
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