moscow russia thursday set dispute u.n. western allegations syrian government behind deadly chemical attack opposition-held town khan sheikhoun april kill dozens report send unite nations security council last week conclude syrian president bashar al-assad government responsible attack prompt u.s. missile strike syrian air base russia whose air force special force support syrian army say time evidence show damascus responsible chemicals kill civilians belong rebel assad government thursday aid map satellite footage chart moscow set believe syrian government unfairly malign russian defence ministry official tell media brief syrian su-22 jet accuse drop chemical bomb physically close enough attack site involve thus believe information provide confirm use chemical weapons khan sheikhoun form aviation bomb drop syrian air force su-22 jet ria news agency quote official name say mikhail ulyanov head russian foreign ministry department non-proliferation arm control tell brief u.s. accusations russia encourage use chemical weapons syria ungrounded ria report hysteria completely open attempt discredit russia rather primitive dirty mean ulyanov quote say white house wednesday admonish russia veto unite nations plan continue ongoing investigation use chemical weapons syria syria agree destroy chemical weapons 2013 deal broke russia unite state syrian government repeatedly deny use chemical weapons country six-year civil war russia set think u.n. wrongly accuse syria sarin attack