A Syrian rebel tries on a gas mask seized from a Syrian army factory in the northwestern province of Idlib on July 18, 2013. Western countries say they have handed over evidence to the UN that Bashar al-Assad's forces have used chemical arms in the two-year conflict. More than 100,000 people have died in the conflict, which morphed from a popular movement for change into an insurgency after the regime unleashed a brutal crackdown on dissent.