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The CEO of United Airlines apologized to customers on Monday following an incident on an overbooked flight where video appeared to show an elderly man being dragged from his seat and through the aisle of a plane.

Several videos posted on social media appeared to show three law enforcement officers pull a screaming man from his seat on the plane and then drag him by the arms down the aisle as shocked passengers look on. A witness told NBC News the ordeal began after the airline said the flight was overbooked and asked four customers to leave the plane and take a flight the following day.

“This is an upsetting event to all of us here at United,” CEO Oscar Munoz said in a statement. “I apologize for having to re-accommodate these customers. Our team is moving with a sense of urgency to work with authorities and conduct our own detailed review of what happened.”

“We are also reaching out to this passenger to talk directly to him and further address and resolve this situation,” he added in the statement.

The Chicago Department of Aviation said in a statement Monday afternoon that the incident was "not in accordance with" standard operating procedure and the officer's actions were "not condoned" by the department. The officer involved was placed on administrative leave effective Monday pending review of the situation, the department said.

The Chicago Police Department said in a statement earlier Monday that around 6 p.m. on Sunday, a 69-year-old passenger "became irate" after he was asked to leave the plane.

"The passenger in question began yelling to voice his displeasure at which point Aviation Police were summoned," police said in the statement.

A man wearing a security jacket stands in the aisle before a United Airlines passenger is forcibly removed from a plane at O'Hare International Airport in Chicago on Sunday, April 9, 2017. Tyler Bridges / Twitter

Police claimed the officers were attempting to carry the man off the flight "when he fell."

"His head subsequently struck an armrest causing injuries to his face," police said, adding that the man was taken to a hospital and treated for non-life threatening injuries. An investigation into the incident was still ongoing.

Multiple attempts to reach the Department of Aviation for comment were not immediately returned.

Tyler Bridges, who posted video of the incident on Twitter, told NBC News he and his wife were on the United plane at O'Hare International Airport from Chicago to Louisville on Sunday when a flight attendant said the flight was overbooked and four people would have to leave to make room for airline employees.

Bridges said the flight attendant offered an $800 voucher for anyone who would volunteer to get off the flight and leave the following day at 3 p.m.

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"Nobody moved, nobody got up," he said.

When no one volunteered, Bridges said, a gate agent told them the airline had used an algorithm to randomly select four people to get off the plane.

First, a young couple was asked to leave and, “they’re not happy, but they get off. No problem,” Bridges said.

Then the unidentified man in the video was asked to leave, Bridges said.

"He says he's a doctor and has to be in Louisville in the morning to see patients,” he said. “He says he can't be delayed a day."

The agent then said if the man did not leave, she was going to call security, according to Bridges.

Related: Internet Erupts After United Airlines Boots Girls for Wearing Leggings

The man refused, prompting a verbal exchange with law enforcement officers, Bridges said.

One of them "walks down the aisle and starts yelling at the man. He grabs him, throws him out of his seat and they drag him off," Bridges said.

"Everyone is disturbed," Bridges said. "It was kind of a dramatic scene."

After the man was dragged away, the four United employees boarded the flight, he said.

But a few minutes later, the man who was removed from the flight ran back on the plane, saying he needed to get back home.

"Somehow he got back on," Bridges said. "He runs back on — dazed, bloodied, kind of in a mess — yelling 'I have to get home, I have to get home.'"

The man was removed on a stretcher, “resisting the whole time,” Bridges said.

It was unclear how the man returned to the plane and what happened after he was removed.

United confirmed in a statement late Sunday that a passenger was removed from the overbooked flight.

“Flight 3411 from Chicago to Louisville was overbooked. After our team looked for volunteers, one customer refused to leave the aircraft voluntarily and law enforcement was asked to come to the gate,” the company said in a statement.

We are here to keep you #united Dragging is strictly prohibited pic.twitter.com/CSjZD7fM4J — Royal Jordanian (@RoyalJordanian) April 10, 2017

The company apologized for the overbooking situation and referred additional comment to authorities.

Bridges said passengers felt the man had been wronged.

"Airlines overbook flights all the time — that's not uncommon," Bridges said. "But everyone felt that they had wronged the man."

The flight was delayed three hours as a result of the incident, he added.

The incident comes just two weeks after United faced a public relations storm after two girls who were traveling as family or friends of airline employees were denied entry on a flight for wearing leggings.