Two security officers in the US have been discharged after a man was forcibly removed from a United Airlines flight earlier this year.

The Chicago Office of the Inspector General (OIG) found three Chicago Department of Aviation (CDA) security officers and one aviation security sergeant violated rules during the incident.

Dr David Dao was taken off the United Airlines service back on April 9th, after he was asked to give up his seat.

Footage of Dr Dao being dragged from the cabin went viral.

@united @FoxNews @CNN not a good way to treat a Doctor trying to get to work because they overbooked pic.twitter.com/sj9oHk94Ik

— Tyler Bridges (@Tyler_Bridges) April 9, 2017

United Airlines CEO Oscar Munoz apologised for the incident on the overbooked flight in Chicago.

The OIG investigation found the first security officer "escalated a non-threatening situation into a physically violent one" by forcefully removing the passenger.

It said the use of excessive force caused the passenger to hit his face on an armrest, resulting in him sustaining a concussion, a broken nose, and the loss of two teeth.

The investigation also established that the second officer made "misleading statements" in two reports, and a third officer made "material omissions" in a report regarding the first officer's forceful removal of the passenger.

The OIG also said the sergeant "deliberately removed material facts" from the third officer's report, and approved reports without all the essential information.

The Chicago Department of Aviation has discharged the first security officer and the sergeant.

While five-day suspensions were given to the second and third security officers.