The Department of Transportation said it will review the incident, in which a passenger was forcibly removed from the Louisville, Kentucky-bound United flight 3411 at Chicago O’Hare International Airport.
The incident has prompted one security officer’s suspension and created a publicity nightmare for United.
Several passengers recorded the incident on their phones and posted video on social media showing three Chicago Department of Aviation security officers dragging the man, who has not been identified, down the aisle by the arms and legs while other passengers shout in protest. He continued to resist after he was removed and ran back onto the airplane, face bloodied from the encounter.
In a letter to employees, Oscar Munoz said he was “upset to see and hear about what happened”.
But he said that the passenger had been “disruptive and belligerent”.
The airline earlier said that it was investigating what happened after videos provoked a social media outcry.