Washington has not ruled out military strikes. In April last year, the US fired cruise missiles at a Syrian airbase after a Sarin nerve agent attack on the opposition-held town of Khan Sheikhoun killed more than 80 people. International investigators held the Syrian government responsible.
What happened on Saturday?
The Syrian-American Medical Society said more than 500 people were brought to medical centres in Douma, in the Eastern Ghouta region, near the capital Damascus, with symptoms “indicative of exposure to a chemical agent”.
It said this included breathing difficulties, bluish skin, mouth foaming, corneal burns and “the emission of chlorine-like odour”.
Neither the death toll nor what exactly occurred can be verified as the area is blocked off with access denied.
The estimates of how many people died in the suspected chemical attack range from 42 to more than 60 people, but medical groups say numbers could rise as rescue workers gain access to basements where hundreds of families had sought refuge from bombing.