Syria's main opposition group on Sunday urged the United Nations to probe "numerous massacres" they say were committed by President Bashar al-Assad's forces during the Muslim fasting month of Ramadan.

The National Coalition also said it was ready to cooperate in any independent investigation into alleged crimes committed by opposition forces.

The Coalition's call comes two days after UN rights chief Navi Pillay said a reported mass execution by rebels of Syrian soldiers taken captive in the northern town of Khan al-Assal should be investigated.