Even the rebels’ U.S. supporters appear to be more cautious in their statements after a series of hits to the opposition forces’ credibility: purported videos of regime crimes that were revealed as fakes, exaggerations in reports of mass killing by government forces, the spread of militant Islamists in rebel ranks, U.N. claims of cease-fire violations and, now, potential atrocities such as prisoner executions.

“We strongly condemn summary executions by either side in Syria. We condemn actions like that,” White House Press Secretary Jay Carney told reporters this week. He quickly added, however, that it was Assad’s forces “that have perpetrated the overwhelming amount of violence in Syria.”

Earlier this week, fighters in a rebel-held suburb of Damascus stopped and interrogated three men driving through the area on suspicion that they were government informants. After being held for several hours, the men were released, having proved their identity to the rebels’ satisfaction.

Other suspects haven’t been so lucky, explained a rebel commander in Damascus who uses the nom de guerre Abu Abdullah.

“We have had a big problem here with informers,” he said. “If a man is accused of being an informer, he is judged by the military council. Then he is either executed or released. In general, about two out of three are executed.”

Abu Abdullah said that the council had ordered the executions of some 150 men since the beginning of the conflict, but that the rate had declined as the rebels feel the neighborhood is “cleaned” of pro-regime elements.

“In the beginning, we would execute 10 or 15 men a week,” he said. “Now it’s closer to one every 10 or 20 days.”

At least some rebel elements appear keenly aware that their moral high ground is in danger of being challenged and have issued statements in recent days vowing to abide by international conventions governing battlefield conduct. However, the Free Syrian Army remains only loosely organized, with no true central command, and it’s impossible to tell which – if any – units are enforcing such orders.

In one video, posted Monday on YouTube, a self-proclaimed representative of the Free Syrian Army read a statement announcing that, in response to international concerns, units would adhere to the Geneva Convention’s guidelines for the treatment of prisoners and would guarantee its captives food, medical attention and holding areas away from active combat zones. The rebel spokesman also invited Red Cross workers to inspect their detention facilities.

“We tell everyone that we are revolting against a barbarous regime that always tortured and treated detainees and arrestees in brutal ways that led to the deaths of many,” the rebel says in the video. “That’s why we can never adopt the behavior of that very entity that we are revolting against.”

International humanitarian organizations and conflict monitoring agencies have become more vocal in criticizing rebel forces for battlefield transgressions, warning them against tit-for-tat violence that would only fuel the civil strife.

One, the International Crisis Group, a nonprofit monitor of global conflicts, called on the rebels to assume responsibility for halting revenge killings.

“The regime almost certainly will not change its ways, so the burden must fall on the opposition to do what – given the immensity of its suffering – must seem an improbable undertaking: seriously address the phenomena of retaliatory violence, sectarian killings and creeping fundamentalism within its ranks,” the group in a report released Wednesday titled “Syria’s Mutating Conflict.”

The group also recommended that the opposition rethink the goal of total regime change and focus on rehabilitating current institutions. To reassure Assad’s minority Alawite sect, so far the backbone of his support, and other regime loyalists, the opposition should “come up with forward-looking proposals on transitional justice, accountability and amnesty,” the report said.