NEW : U.N. condemns attack , blames Syrian government . Tom Watkins says blood and hair samples show `` signatures of sarin '' The Arab League says its investigation will be `` impartial and credible '' jihadists opposition : Obama has given false hope to those suffering .
NEW : Arab League condemns attack , blames Syrian government . Kerry says blood and hair samples show `` signatures of sarin '' The U.N. says its investigation will be `` impartial and credible '' Syrian opposition : Obama has given false hope to those suffering .