The US State Department has reported indications that a toxic industrial chemical, probably chlorine, was used in the Syrian town of Kfar Zeita this month.
"We have indications of the use of a toxic industrial chemical" US spokeswoman Jen Psaki said, referring to the rebel-held area in the central province of Hama.
Psaki said the United States was still trying to determine the facts and that "there needs to be an investigation of what's happened here."
More top news
A nurse has told ITV News how the courage of the Manchester bombing victims gave her the strength to carry on.
A warm evening with late sunshine and feeling very summery
Donald Trump has threatened to "Send in the Feds" to deal with gun and gang problems but many say that deeper changes are needed.