A chemical attack on Douma took place on 7 April 2018 that killed at least 49 civilians with scores injured, and which has been blamed on the Assad government. On 10 April, the Syrian and Russian governments invited the OPCW to send a team to investigate the attacks. The investigators arrived in Damascus on April 14, but were blocked from entering Douma, saying they can not guarantee their safety. Under the evacuation agreement for Ghouta, the Syrian military were unable to enter Douma, so Russian Military Police assisted the OPCW mission. Concerns were also raised by US ambassador Kenneth D. Ward that Russia was trying to conceal the evidence, and that Russia had tampered with the site of the attack to thwart the OPCW fact finding mission; Russian Foreign Minister Sergei Lavrov denied any tampering had occurred.