US President Donald Trump has promised a "forceful" response to the alleged chemical attack in Syria, as Western leaders consider what action to take.
Mr Trump said the US was getting some "good clarity" on who was responsible for the incident in Douma on Saturday.
Medical sources say dozens were killed in the alleged attack but exact numbers are impossible to verify.
Mr Trump also discussed the incident with French President Emmanuel Macron late on Monday, and both leaders expressed a desire for a "firm response".
UK Prime Minister Theresa May has said she "utterly condemns" the "barbaric" alleged chemical weapons attack and called for backers of President Bashar al-Assad to be held to account.
Read more: Syria 'chemical attack': Trump pledges 'forceful' US response - BBC News