On 7 April 2018, a chemical attack in the Syrian city of Douma reportedly killed at least 70 people. It was unclear what chemical had been used. Medics on the ground reported smelling a chlorine-like substance, but said the patients' symptoms and the large death toll pointed to a more noxious substance such as nerve agentsarin. The attack was attributed to the Syrian Army by rebel forces in Douma, non-governmental aid and medical workers there, and by a number of countries, including the United States, most NATO members, and the European Union. Syria and Russia's defense ministries stated that "the attack did not happen and video evidence for it was staged and directed by British intelligence".
On 14 April 2018, the United States, France and the United Kingdom carried out a series of military strikes against multiple government sites in Syria.
On 6 July 2018 an interim report was issued by the Organisation for the Prohibition of Chemical Weapons (OPCW). Various chlorinateorganic chemicals (dichloroacetic acid, trichloroacetic acid, chlorophenol, dichlorophenol, bornyl chloride, chloral hydrate etc.) were found in samples, along with residues of explosive, but the designated laboratory 03 stated that no CWC-scheduled chemicals or nerve agent related chemicals were detected. In September 2018 the UN Commission of Enquiry on Syria reported: "Throughout 7 April, numerous aerial attacks were carried out in Douma, striking various residential areas. A vast body of evidence collected by the Commission suggests that, at approximately 7.30 p.m., a gas cylinder containing a chlorine payload delivered by helicopter struck a multi-storey residential apartment building located approximately 100 metres south-west of Shohada square. The Commission received information on the death of at least 49 individuals, and the wounding of up to 650 others."
Douma had been under rebel control since 18 October 2012, and, with the rest of the Eastern Ghouta region, under siege since April 2013. The Rif Dimashq offensive (February–April 2018), code-named Operation Damascus Steel, a military offensive launched by the Syrian Arab Army (SAA) and its allies on 18 February 2018 to capture the rebel-held territory. The Jaysh al-Islam rebel coalition controlled Douma. By mid-March, rebel territory in Eastern Ghouta had reduced to three pockets, one in the south around Hamouria held by Faylaq al-Rahman; a second in the west around Harasta held by Ahrar al-Sham; as well as Douma in the north held by Jaysh al-Islam. In the second half of March, the other two pockets were secured via evacuation deals between the rebels, Syria, and Russia. On 31 March, the last of the evacuations was conducted and the Syrian army declared victory in Eastern Ghouta, while the rebels that were still holding out in Douma were given an ultimatum to surrender by the end of the day.