Opposition members claim that the clip, of unknown origin, was filmed on the roof of a mosque in the southern town of Dara'a, where anti-government protests first erupted.
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The full-length film, which is not shown here, includes horrifying footage of soldiers entertaining each other with snide remarks.
"Your father told you to watch out, but you didn't," one soldier says to a corpse of a man who apparently took a bullet to the head from close range.
Al-Arabiya aired parts of the clip, with the victims' faces blurred and a disclaimer regarding its origins. But the full-length clip has already received 20,000 hits on YouTube.
Barak predicts: Assad will fall
Meanwhile, Syrian activists are accusing security forces of murdering the victims "in cold blood", the London-based al-Sharq al-Awsat reported Monday.
The film "proves these people belong to armed gangs," the report cites activists as saying. However it also proves that there is discord among the troops and that some are refusing to go along with the regime's orders, they added.
Defense Minister Ehud Barak predicted that Syrian President Bashar Assad has been irreparably weakened by the popular uprising. "I think Assad will fall," Barak told Israel Radio on Monday.
The instability in Syria, Barak said, rules out prospects for renewing peacemaking. Israel and the Syrians last held talks in 2008, but they broke down upon the outbreak of Operation Cast Lead.
AP contributed to this report
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