(CNN) -- The Syrian ambassador to the U.N., Bashar Jaafari, has asked the U.N. secretary-general to launch an investigation into what Syria claims was the use of chemical weapons Tuesday by "terrorist groups" in Khan al-Asal, Syria, Jaafari said Wednesday. The opposition Free Syrian Army earlier said rebels don't have access to chemical weapons, and another opposition group accused the Syrian government of launching "chemical rockets" against the town of Ateibeh.