Turkey says a red line has been crossed
23 August 2013 Last updated at 03:28 BST
UN Secretary-General Ban Ki-moon has said the alleged chemical weapons attack near the Syrian capital "needs to be investigated without delay".
He is sending disarmament chief Angela Kane to Damascus to press for an investigation, his spokesman Eduardo del Buey said on Thursday.
Turkish Foreign Minister Ahmet Davutoglu has also stressed the need for an urgent response, and criticised the lack of UN action. He told Newsnight's Victoria Derbyshire that it is "not the first time Assad has crossed red lines".