U.S. Defense Secretary Jim Mattis said on Friday that while he had not yet seen evidence of the nerve agent sarin used by the Syrian government, the United States was looking into reports about its use and was concerned.
Mattis, speaking with reporters, said the Syrian government had repeatedly used chlorine as a weapon.
"We are even more concerned about the possibility of sarin use... I don't have the evidence, what I am saying is, that other groups on the ground, NGOs, fighters on the ground, have said that sarin has been used, so we are looking for evidence," Mattis said.
