Lebanon's army on Thursday handed over a group of soldiers accused of abusing a detainee to the military police for questioning, a military source and the National News Agency said.
The move came after amateur video emerged showing a group of soldiers humiliating, beating and kicking a man suspected of supporting a radical Sunni cleric whose men fought troops near the southern city of Sidon.
"The group of soldiers behind the beating of a civilian in Sidon has been detained by the military police and is now being investigated," the NNA said.
A military source confirmed the report, adding: "We do not accept this kind of behaviour."
Soldiers battled supporters of Sheikh Ahmad al-Assir in Abra near Sidon last weekend in a major gun battle lasting 24 hours.
Assir is now on the run after 18 soldiers were killed in the clash.
Earlier on Thursday, the army said it had ordered a "major investigation" into the beating of a suspect.
The video footage shows the man saying he worked in Assir's mosque, but that he has no weapons and had nothing to do with the fighting.
"I have no weapons... I don't like him (Assir), may God curse him," says the man, visibly afraid.
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"Liar!" cries a soldier.
Wearing a white T-shirt, the suspect is seated cross-legged on the ground, with around a dozen troops surrounding him.
The video shows one man in civilian clothing hitting him, then a soldier kicking him and finally several others joining in.
A man is heard ordering those filming with their telephones to stop, and the footage ends abruptly.
The Abra clash was the worst in Lebanon since the outbreak of conflict in neighbouring Syria 27 months ago has deepened sectarian tensions.
Although Assir's extremist discourse was unpopular with members of his Sunni sect, the army's campaign against him raised questions over why the military failed to use the same force against the powerful Shiite movement Hezbollah.
Sunni clerics have accused the army of covering for Hezbollah, whose troops are fighting alongside President Bashar al-Assad's forces in Syria.
Relatively unknown just two years ago, Assir gained prominence in Lebanon because of his virulently anti-Hezbollah, sectarian discourse.
In a separate development, Hezbollah evacuated two apartments in Abra on Thursday near Assir's headquarters, after the cleric had accused it of stocking arms there and of spying on him.
"We have evacuated the buildings in order to keep the peace in the area," a Hezbollah source told AFP on condition of anonymity.
A military source confirmed the report.