After a somewhat mealy-mouthed first effort appeared to fall on deaf ears, United Airlines chief executive Oscar Munoz has issued a second apology following the forced removal of a passenger from a flight.

Passenger David Dao was dragged screaming from a flight from Chicago to Louisville, Kentucky, on Sunday, with the airline initially describing the flight as overbooked.

However, it has since emerged United sought to remove four passengers in order to accommodate members of staff who were needed in Louisville the next day.

After initially branding the incident “upsetting”, Munoz has now upgraded to “truly horrific”.

In a statement he explained: “The truly horrific event that occurred on this flight has elicited many responses from all of us: outrage, anger, disappointment.

“I share all of those sentiments, and one above all: my deepest apologies for what happened.

“Like you, I continue to be disturbed by what happened on this flight and I deeply apologise to the customer forcibly removed and to all the customers aboard.

“No one should ever be mistreated this way.”

Dao argued he worked in a hospital and needed to see his patients the next day, eyewitnesses reported.

A video posted to YouTube appears to show him dazed and with blood around his mouth, saying “just kill me”, having run back on the plane.

Dao’s family issued a statement saying he “wants the world to know that they are very appreciative of the outpouring of prayers, concern and support they have received”.

One of the aviation security officers involved in removing Dao from the plane has been placed on leave, the Chicago Department of Aviation said.

His actions were “obviously not condoned by the department,” a statement added.

Munoz added in his apology: “It’s never too late to do the right thing.

“I have committed to our customers and our employees that we are going to fix what’s broken so this never happens again.

“This will include a thorough review of crew movement, our policies for incentivizing volunteers in these situations, how we handle oversold situations and an examination of how we partner with airport authorities and local law enforcement.”

The results of the review would be made public by the end of April, he concluded.

Take a look below for footage of the incident:

@United overbook #flight3411 and decided to force random passengers off the plane. Here's how they did it: pic.twitter.com/QfefM8X2cW

— Jayse D. Anspach (@JayseDavid) April 10, 2017