(CNN) The mistaken US-led coalition bombing of a Syrian military position Saturday may have happened because the personnel weren't wearing military uniforms and didn't have standard military weapons, several US military officials told CNN.

Officials said they now think the personnel bombed may have been Syrian military prisoners, according to several US defense officials.

That's a working theory of how US, British, Danish and Australian aircraft may have incorrectly assessed intelligence and targeted the site that killed more than 60 Syrian personnel near Deir Ezzor in eastern Syria. The UK Ministry of Defence is saying it used drones in the strike.

Officials emphasized there are no final conclusions by the US about who was struck. Overhead imagery and interviews with those involved will have to be assessed.

But the US is not disputing that Syrian personnel were hit. The US is trying to determine what specifically led to the mistaken strike and how the personnel may have been misidentified.

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