The official offered circumstantial elements to back up his claim, but no concrete proof. And others in the Trump administration cautioned that final American determination had been made that Russia had advance knowledge of the attack, which killed more than 80 people and prompted retaliatory US cruise missile strikes.
The senior official said yesterday 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, who wasn't authorised to speak publicly on intelligence matters and demanded anonymity, didn't give precise timing for when the drone was in the area. The official also didn't provide details for the military and intelligence information that form the basis of what the Pentagon now believes.
A senior White House official later said there is "no US intelligence community consensus" yet on when Russia might have known of the attack. That official refused to be quoted by name, even though President Donald Trump has criticised the media for citing anonymous sources.
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Although Russia has steadfastly supported Syrian President Bashar al-Assad's government, and they've coordinated military attacks together, Washington has never previously accused Moscow of complicity in any attack that involved the gassing of innocent civilians, including children. The former Cold War foes even worked together in 2013 to remove and destroy more than 1,300 tons of Syrian chemical weapons and agents.
Until yesterday, US officials had said they weren't sure whether Russia or Syria operated the drone. The official said the US is now convinced Russia controlled the drone. The official said it still isn't clear who was flying the jet that bombed the hospital, because the Syrians also fly Russian-made aircraft.
Last Thursday, 59 Tomahawk missiles were fired on the government-controlled base in the United States' first direct military action against Assad's forces.