"We do know that some sort of a substance was used," Nauert told reporters. "A chemical was used, we’re just not sure at this point today exactly what was used."
Nauert explained the United States will rely on information collected by the Organization for the Prohibition of Chemical Weapons (OPCW) regarding the alleged chemical attack, but said the US government also has its own mechanisms to investigate the incident.
Trump blamed Syrian President Bashar Assad for the incident, but said Russia and Iran were also responsible because they support the Syrian government. On Monday, Trump said his administration would make a major decision within the next 24 to 48 hours on what the US response will be.
The Russian reconciliation center for Syria on Sunday categorically refuted the media reports that the Syrian military dropped a chlorine-filled bomb on Duma. The Russian Foreign Ministry said such erroneous information aims to cover the actions of terrorists and justify possible external military intervention in Syria.