United Nations experts are investigating allegations that rebels killed dozens of Syrian soldiers in a village near Aleppo after they captured it from government troops, an incident that could amount to a war crime, the world body's human rights chief said.
Navi Pillay on Friday said in a statement that a UN team in the region is looking into reports about killings that followed the battle in Khan al-Assal in July.
Pillay said the team has examined activists' videos and collected accounts from people in Aleppo on an incident that she called "deeply shocking".
While abuses by troops loyal to President Bashar al-Assad have been systematic and widespread throughout the two-year conflict, human rights groups have said the frequency and scale of rebel abuses also has increased in recent months.
Specific allegations against opposition fighters include claims that rebels have routinely killed captured soldiers and suspected regime informers.
Rebels say any such violations are condemned and an unfortunate result of the government crackdown.
Opposition fighters in recent weeks have suffered major setbacks on the battlefield. Infighting among various armed groups also has plagued rebel ranks, weakening the opposition's campaign against Assad's rule.
Rebels 'not immune'
The capturing of Khan al-Assal on July 21 was overshadowed by activists' claims that rebels had killed 150 government soldiers after taking the village.
Some of the soldiers who were killed had surrendered to the rebels, the Britain-based Observatory for Human Rights reported.
Syrian state media reported that rebels killed 123 "civilians and military personnel" in Khan al-Assal.
In a statement issued in Geneva, Pillay said two of the videos the UN team reviewed apparently show government soldiers being ordered to lie on the ground, while another shows several bodies scattered along a wall and a number of bodies at an adjacent site.
Preliminary findings of the UN probe also suggests that armed opposition groups, in one incident documented by video, executed at least 30 individuals, the majority of whom appeared to be soldiers, Pillay said.
"These images, if verified, suggest that executions were committed in Khan Al-Assal," Pillay said. She called for a "thorough independent investigation to establish whether war crimes have been committed".
She also warned that opposition forces "should not think they are immune from prosecution".
Syria's main opposition bloc last week condemned the killings and blamed the killings on "armed groups" not affiliated with the Western-backed Syrian National Coalition. The umbrella group of opposition fighters is known as the Free Syrian Army.
In-depth coverage of escalating violence across Syria
Self-proclaimed jihadist groups have been gaining influence and groups such as the al-Qaeda-linked Jabhat al-Nusra have led major battles in the past year.
In a statement last week, Jabhat al-Nusra confirmed its fighters had participated in the battle for Khan al-Assal.
The group has not claimed responsibility for the soldiers' killings, though it did confirm in a statement last week that 150 soldiers, pro-government gunmen and Shia fighters were killed in Khan al-Assal.
More than 100,000 people have been killed since March 2011 when crisis started with largely peaceful protests against Assad's rule. It turned into civil war after opposition supporters took up arms to fight a brutal government crackdown on dissent.
Millions have been fled their homes, with some seeking shelter in more peaceful parts of Syria and more than a million fled into neighboring countries.