US National Security Adviser H.R. McMaster said on Saturday that, despite denials, public reports showed that Syrian President Bashar al-Assad was using chemical weapons, and added that it was time for the international community to hold the Syrian government to account.
"Public accounts and photos clearly show that Assad's chemical weapons use is continuing," McMaster said at a major international security conference taking place in Munich.
"It is time for all nations to hold the Syrian regime and its sponsors accountable for their actions and support the efforts of the Organization for the Prohibition of Chemical Weapons," he said.
McMaster did not specify which public accounts or pictures he was referring to.
Earlier this month, US Defense Secretary Jim Mattis said the Syrian government had repeatedly used chlorine gas, but stressed that the US did not have evidence of sarin gas use.
French President Emmanuel Macron has said that, "France will strike" if chemical weapons are used against civilians in the Syrian conflict in violation of international treaties, but that he had not yet seen proof this is the case.
The Syrian government has repeatedly denied using chemical weapons and said it targets only armed rebels and militants.
In recent weeks, rescue workers, aid groups and the United States have accused Syria of repeatedly using chlorine gas as a weapon against civilians in Ghouta and Idlib.
Earlier this month, Syrian government forces, which are backed by Russia and Iran, bombarded the regions, two of the last major rebel-held parts of Syria.