Three law enforcement officers who dragged a doctor off a United Airlines' flight in April are no longer in their jobs. Two officers were sacked, while the third officer resigned.

An officer and an aviation security sergeant involved in the "violent forcible removal" of doctor David Dao were fired from their jobs by the Chicago Department of Aviation.

In a report released on Tuesday (17 October), Chicago's inspector general Jospeh Ferguson said a third officer resigned and a fourth received a five-day suspension, which was shortened to two days following an appeal.

The security officer was also allegedly part of an attempt to cover up some of the incident, The Associated Press reported. The officers made misleading statements and "deliberately removed material facts from their reports", the investigation found.

According to NBC News, Ferguson's report stated that "excessive force" led Dao to break his nose, lose two teeth and sustain a concussion. The report noted that the security officer who pulled Dao from the flight broke department policy by escalating "a nonthreatening situation into a physically violent one".

The identities of the four officers were not revealed in Ferguson's report.

United Airlines came under fire after video showed Dao being forcibly dragged from the flight at Chicago's O'Hare International Airport. The incident led to a lawsuit and settlement by the airline in late April.

The Aviation Department said a review of its policies and procedures was ongoing and would be completed by the first quarter of 2018, The Chicago Tribune reported.

"As we have clearly stated, the department is taking every action in our power to ensure that an incident like this never, ever occurs again," aviation spokeswoman Lauren Huffman said.