US media say the US military was unable to stop the deadly drone attack on its base in Jordan, as an enemy drone approached at the same time that a US drone was also returning there.
Three US service members were killed in the attack at the outpost in northeastern Jordan near the border with Syria on Sunday.
The US government suspects that the attack was carried out by Iran-backed militant groups operating in Syria and Iraq.
The Wall Street Journal on Monday quoted senior US officials as saying that the US failed to stop the deadly attack when "the enemy drone approached its target at the same time a US drone was also returning to base."
The officials reportedly said that "the return of the US drone led to some confusion over whether the incoming drone was friend or foe."
CNN said that the enemy drone approached the US military outpost while following the American drone.
Deputy Pentagon Press Secretary Sabrina Singh told reporters on Monday that officials are still assessing how a one-way attack drone was able to impact the facility.
She said that it has the footprints of the pro-Iranian militant group Kataib Hezbollah, but added the Pentagon has not made a final assessment on that.