US President Donald Trump has cancelled his first official trip to Latin America to focus the response to a suspected chemical attack in Syria.
He will remain in Washington to “oversee the American response to Syria”, the White House said.
Vice-President Mike Pence will travel in his place to Peru for the Summit of the Americas and then Colombia.
Medical sources say dozens were killed in the alleged attack in Douma, but exact numbers are impossible to verify.
Syria and its military backer Russia have denied any involvement in Saturday’s incident. They have invited inspectors from the Organisation for the Prohibition of Chemical Weapons to visit Douma.
Mr Trump has pledged a “forceful” response, and has spoken of numerous military options.
Washington has been in discussion with Britain and France, raising the prospect of co-ordinated Western military action.
France says poison gas was deliberately used in Douma, in the Eastern Ghouta region outside Damascus, as it could seep down to the basements where people were sheltering from bombardment.