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US Official: Russia knew Syrian chemical attack was coming

FILE - 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.  (Edlib Media Center, via AP)

FILE - 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‚Äôs chemical weapons attack last week. (Edlib Media Center, via AP)  (The Associated Press)

The United States has made a preliminary conclusion that Russia knew in advance of Syria's chemical weapons attack last week, but has no proof of Moscow's involvement. That's according to a senior U.S. official.

The official said Monday that a drone operated by Russians was flying over a hospital as victims of the attack were rushing to get treatment. Hours after the drone left, a Russian-made fighter jet bombed the hospital in what American officials believe was an attempt to cover up the usage of chemical weapons.

The official said the presence of the surveillance drone over the hospital couldn't have been a coincidence.