Following the August 2013 Ghouta chemical attack, Syria, which had long been suspected of possessing chemical weapons, acknowledged them in September 2013 and agreed to put them under international supervision. On 14 September Syria deposited its instrument of accession to the CWC with the United Nations as the depositary and agreed to its provisional application pending entry into force effective 14 October. An accelerated destruction schedule was devised by Russia and the United States on 14 September, and was endorsed by United Nations Security Council Resolution 2118 and the OPCW Executive Council Decision EC-M-33/DEC.1. Their deadline for destruction was the first half of 2014. Syria gave the OPCW an inventory of its chemical weapons arsenal and began its destruction in October 2013, 2 weeks before its formal entry into force, while applying the convention provisionally. All declared Category 1 materials were destroyed by August 2014. However, the Khan Shaykhun chemical attack in April 2017 indicated that undeclared stockpiles probably remained in the country. A chemical attack on Douma occurred on 7 April 2018 that killed at least 49 civilians with scores injured, and which has been blamed on the Assad government.