UN Syria envoy Staffan de Mistura said today that a "horrific" attack on a rebel-held town in the country that killed at least 58 people was believed to be chemical and launched from the air. <br/><br/>De Mistura told reporters in Brussels that there should be a "clear identification of responsibilities and accountability.'<br/>'<br/>De Mistura, fresh from the latest round of UN-sponsored peace talks in Geneva between the rebels and Damascus, said that every time there was a sign of progress, someone- unnamed- always tried to sabotage it. <br/><br/>He was speaking on the sidelines of a Syrian aid conference in Brussels.'<br/>'<br/>Separately, the UN Commission of Inquiry for Syria said it had begun investigating the attack on a rebel-held town in northwestern Idlib Province.'<br/>'<br/>The Organisation for the Prohibition of Chemical Weapons (OPCW), based in The Hague, meanwhile also said it was gathering and analysing information from all available sources about the attack.