moon and the head of the Organization for the Prohibition of Chemical Weapons (OPCW) are concerned at the possibility that Syria may have chemical weapons, a UN spokesman said on Thursday. “On Syria, the Secretary-General and the Director-General noted with concern the reports on the possible existence of chemical weapons in the country,” UN spokesman Martin Nesirky told reporters. “Those concerns are entirely understandable.” Top US military officer, General Martin Dempsey, chairman of the US military's Joint Chiefs of Staff, said last week that Syria is “very capable,” with a sophisticated, integrated air defense system and chemical and biological weapons. An 11-month government crackdown on pro-democracy protesters has left an estimated 7,500 civilians dead, according to the United Nations, and the outside world has proved powerless to halt the killing. Defeated Syrian rebels left their shattered stronghold in the city of Homs on Thursday after a bloody 26-day army siege aimed at crushing a symbol of the year-long revolt against President Bashar Al-Assad. Activists said a few fighters had stayed on in the Baba Amro district, which has endured weeks of shelling, sniper fire and privation, to cover their comrades' “tactical withdrawal”. Soon afterward, the international Red Cross said Syrian authorities had finally given it permission to take aid into the district on Friday. “The Free Syrian Army and all the other fighters have left Baba Amro,” one activist said from Homs. “They pulled out.” A pro-government figure proclaimed that troops had “broken the back” of the rebellion and that the fall of Baba Amro heralded impending victory over a Western-backed insurgency. A statement in the name of the fighters urged the International Committee of the Red Cross and other humanitarian groups to enter Baba Amro to protect and bring aid to 4,000 civilians who had stayed in their destroyed houses. “We warn the regime against any retaliation against civilians and we hold it fully responsible for their safety,” the statement said, adding that the rebels had been forced to leave because they were short of supplies and ammunition. Russia and China joined other UN Security Council members in expressing disappointment at Syria's failure to allows UN humanitarian chief Valerie Amos to visit and urged that she be allowed in immediately, France said. The ICRC said it had received a “green light” from the Syrian authorities to enter Baba Amro on Friday. One activist said Syrian soldiers had begun moving into Baba Amro from all directions after most of the fighters left.