UN accuses Syrian rebels of chemical weapons use Western nations have raised concerns about the use of chemical weapons in the escalating conflict between the regime of President Bashar al-Assad and rebels fighting to oust him. Top UN rights investigator Carla del Ponte said Sunday that according to testimony, rebels have been using sarin gas. US President Barack Obama has refused to rule out any options, but has said he did not foresee deploying US troops if Assad's regime is proved to have used chemical weapons. Turkish Prime Minister Recep Tayyip Erdogan, a one-time Syria ally, on Sunday branded Assad a "butcher" and a "murderer" who would pay a heavy price for the killings in Syria. UN Secretary-General Ban Ki-moon appealed Sunday for restraint to avoid an escalation in Syria's civil war, expressing "grave concern" over Israeli air raids. Israel launched air strikes earlier that hit three military sites near Damascus, the second such reported attack in a 48-hour period targeting the transfer of arms to Lebanon-based Hezbollah, raising fresh concerns of a regional spillover. "The secretary-general calls on all sides to exercise maximum calm and restraint, and to act with a sense of responsibility to prevent an escalation of what is already a devastating and highly dangerous conflict," Ban's spokesman Martin Nesirky said in a statement. Nesirky said the United Nations was unable to independently verify the raids, and had no details about them, but Ban "expresses grave concern over reports of air strikes in Syria by the Israeli Air Force." "The secretary-general urges respect for national sovereignty and territorial integrity of all countries in the region, and adherence to all relevant Security Council resolutions," Nesirky said.