A police officer said "minimal but necessary force" was used to remove a United Airlines customer from a plane in what has become a public relations disaster for the company.

Video taken by other passengers showed David Dao, a 69-year-old Vietnamese-American doctor, being dragged up the aisle with blood on his face after the airline decided it needed his seat for a crew member on a flight from Chicago to Kentucky on April 9.

Dao suffered concussion, a broken nose and lost two front teeth and is likely to sue the airline, his lawyer, Thomas Demetrio, has said. In its initial reaction, the airline did not apologise to Dao and described him as "disruptive and belligerent." Social media users in the United States, Vietnam and China called for a boycott.

In an incident reported released by city authorities and posted on the Chicago Tribune's website, aviation police officer Mauricio Rodriguez said Dao had become combative when he and two other officers tried to persuade him to leave the plane.

According to the report, Dao told the officers: "I'm not leaving this flight that I paid money for. I don't care if I get arrested."

An officer identified as James Long then tried to get Dao out of his seat, at which point the passenger "started swinging his arms up and down fast and violently," the report said.

Long lost control of Dao as he swung, causing Dao to fall and hit his mouth on the armrest. Long "assisted the subject by using minimal but necessary force" to get him off the aircraft, Rodriguez said in the report.

Demetrio said through a spokeswoman to the Wall Street Journal that the police version of events was "utter nonsense. Consider the source.”

Chicago's aviation department on Monday told the Journal that the three officers involved remained on leave and that it was conducting an investigation.