Over the last four months, since late 2016, the Syrian government troops have carried out at least four attacks that employed chemical weapons. This was mentioned in the report by Human Rights Watch, as quoted by Al Jazeera.
'The government's use of nerve agents is a deadly escalation. In the last six months, the government has used warplanes, helicopters, and ground forces to deliver chlorine and sarin in Damascus, Hama, Idlib and Aleppo', Kenneth Roth, HRW's executive director, said. 'That's widespread and systematic use of chemical weapons'.
Syrian leader Bashaar al Assad has been denying any involvement in the chemical attacks.
About a hundred civilians were killed and hundreds more injured during the latest strike on Khan Sheykhun, Idlib province, which took place last month.