unite nations syrian government bashar al-assad blame chemical attack opposition-held town khan sheikhoun kill dozens people last april accord report send unite nations security council thursday syrian arab republic responsible release sarin khan sheikhoun april 2017 report u.n. organization prohibition chemical weapons joint investigative mechanism jim say attack prompt u.s. missile strike syrian air base washington say use launch strike time see independent confirmation chemical weapons use assad regime nikki haley unite state u.n. ambassador say statement security council must send clear message use chemical weapons anyone tolerate must fully support work impartial investigators report also say isis blame use sulfur mustard syrian town umm hawsh sept. 15 16 2016. jim unanimously create 15-member u.n. security council 2015 renew 2016 another year mandate due expire mid-november russia tuesday veto proposal extend mandate russian ambassador u.n. vassily nebenzia say early week russia would consider revisit mandate extension thursday report discuss speak beijing chinese foreign ministry spokesman geng shuang say china hop conclusions investigation basis conclusive proof professional objective fair continue use chemical weapons include non-state actors deeply disturb say report use spite prohibition international community stop lack consequences surely encourage others follow jim already find syrian government force responsible three chlorine gas attack 2014 2015. syria agree destroy chemical weapons 2013 deal broke russia unite state syrian government repeatedly deny use chemical weapons country six-year civil war syrian government blame april sarin attack u.n. report