FILE -- This Tuesday April 4, 2017, file photo, provided by the Syrian anti-government activist group Edlib Media Center, that is consistent with independent AP reporting, shows a man carrying a child following a suspected chemical attack, at a makeshift hospital in the town of Khan Sheikhoun, northern Idlib province, Syria. Walid Moallem, Syria's Foreign Minister, told reporters Thursday, April 6, 2017, that it didn't use chemical weapons in Tuesday's attack, and he blamed the rebels for stockpiling the deadly substance. (Edlib Media Center, via AP, File)

WASHINGTON — A senior U.S. official says the United States has concluded that Russia knew in advance of Syria's chemical weapons attack last week.

The official says a Russian-operated drone flew over a hospital in Syria 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.

Until Monday, U.S. officials had said they weren't sure if the drone was operated by Russia or Syria. The senior official said it still wasn't clear who was flying the jet that bombed the hospital.

The official said the presence of the drone couldn't have been a coincidence and that Russia must have known the chemical weapons attack was coming and that victims were seeking treatment.

The official wasn't authorized to speak publicly on intelligence matters and demanded anonymity.

Read Tuesday's Arkansas Democrat-Gazette for full details.