An elite Israel Prison Services ( IPS) unit operating undercover in a Palestinian West Bank village took part in stone throwing incidents against army forces deployed to the area to quell riots, Israeli officials told Xinhua Monday.

The details came to light during recent in-camera testimony by two members of the IPS' Massada unit in the trial of Arab Knesset (parliament) member Mohammed Barakeh, who the army said assaulted a soldier at a demonstration in the village of Bil'in seven years ago.

The Massada unit, more normally tasked with breaking up prison riots, in 2005 operated in the field under IDF command during weekly demonstrations by the village's Palestinian residents and outside supporters against a security fence that cut farmers off from part of their land.

During the weekly protests, hundreds of opponents of the barrier would often hurl firebombs, rocks, and abuse at IDF soldiers deployed to keep the rioters away from the fence. The troops would respond by trying to apprehend the ringleaders, and often firing tear gas and rubbers bullets to drive others away.

"We were sent to counter the disruptions at the separation barrier in Bil'in," one of the officers said in testimony given in a Tel Aviv courtroom two weeks ago. "It was the first time I was undercover. Two men were arrested, they were Palestinians," he said, according to the Ha'aretz daily.

The witness told the defense counsel that, in order to better blend in with the demonstrators, he would also throw stones "in the general direction" of the soldiers.

It was not divulged if any of the troops were hit by stones he had thrown, of if he was hit by the army's counter-measures.

The unit's commander said in his testimony that "an enormous demonstration began, coming down from the village," adding that he had received intelligence information of a major riot brewing on the day in question.

He noted that "we had several forces in the field, one of them was an undercover force whose mission was to provide intelligence and carry out 'quality' arrests," with a uniformed "rescue" force standing by.

"It seemed that the army was losing control," he said. "Some 500 demonstrators came down and ignored the orders of the deputy battalion commander, who was in charge of the operation, and simply passed by him without blinking. The army forces swiftly lost their ability to effectively control the situation," he said.

"When the undercover unit reported, it identified 'quality' targets - that is substantial activists who led the demonstration, hurled stones and constituted a danger to the forces. I ordered the undercover forces to carry out arrests. I caught the back of a man who attacked one of my soldiers, and identified him as MK Barakeh. As far as I'm concerned if an undercover soldier arrested someone, he must be a quality target," the officer said, according to Ha'aretz.

In remarks to Xinhua on Tuesday, IPS Spokesman Sivan Weitzman expressed surprise over the issue's publication, noting that "this took place in 2005, there have been no such operations of this kind since then."

The Israel Defense Forces Spokesman refused specific comment on the incident, stressing that the affair was an IPS issue.