US President Barack Obama has said the alleged use of chemical weapons in Syria in an attack on Wednesday is a “big event of grave concern”.
Mr Obama said the US was still seeking confirmation such weapons were used, but if proved true the situation would “require America’s attention”.
Activists say hundreds died in the alleged chemical attack near Damascus.
But there is no sign yet that Damascus will allow a UN inspection team to visit to investigate the claims.
Unverified footage shows civilians – many of them children – dead or suffering from what appear to be horrific symptoms as a result of Wednesday’s attack.
Also on Friday, UN agencies said the number of children forced to flee Syria had reached one million.
The UN’s refugee agency and Unicef describe the figure as “a shameful milestone”, and say a further two million children are displaced within the country.