The British Prime Minister David Cameron says Syria's President Assad should face an international court.
Mr Cameron is due to arrive at the UN in New York later today, where he will call for greater diplomatic efforts to end the war in Syria.
His visit comes as France joined the bombing campaign, launching its first air strikes against Islamic State militants.
Jonathan Shaw is a former Commander of Forces in Iraq, and welcomes David Cameron's move: "I think what we showed quite clearly in our interventions in Iraq and Afghanistan was that military intervention is only as good as the political plan that it's supporting, and if there's no real political plan then the military intervention is just a fleeting passage of arms."