A United Nations inquiry has found Syrian government forces responsible for a third toxic-gas attack last year, an attack condemned harshly by the White House.
The report, submitted by the UN and the Organization for the Prohibition of Chemical Weapons to the UN Security Council, sets the stage for a showdown between Russia and Western powers over how to respond to the incident.
The report blames Syrian government forces for an attack using toxic gas, probably chlorine, in the Idlib region on March 16, 2015.
In August, the United Nations said the regime of Syrian President Bashar al-Assad was responsible for two other chlorine-gas attacks in the country.
"We condemn in the strongest possible terms the Assad regime's defiance of the long-standing global norm against chemical-weapons use and Syria's abrogation of its responsibilities under the Chemical Weapons Convention," U.S. National Security Council spokesman Ned Price said in a statement on October 22.
Russian "military and economic support to Syria enables the Assad regime to continue its military campaign against its own people," he said.
The report is expected to prompt a fierce debate at the the UN Security Council, pitting Russia and possibly China against the United States, Britain, and France, which are expected to press for censure of the perpetrators.
After Syria was blamed for the earlier two chemical attacks, Russia blocked any action, saying the UN's conclusions could not be used to impose sanctions.
The latest report provided extensive detail on the attacks, saying the Syrian government used helicopters to drop barrel bombs filled with chlorine gas.
Details in the UN investigators' latest report identify the military bases from where the helicopters took off.