In his photo April 4, 2017 file photo, provided by the Syrian anti-government activist group Edlib Media
Center, which has been authenticated based on its contents and other AP reporting, shows victims of a
suspected chemical attack, in the town of Khan Sheikhoun, northern Idlib province, Syria. A senior U.S.
official says the U.S. has concluded that Russia knew in advance of Syria’s chemical weapons attack last
week.