MMA fighter Conor McGregor has been charged with three counts of assault and one count of criminal mischief following a rampage at a UFC press event in Brooklyn on Thursday, the New York Police Department has said.

The 29-year-old turned himself in to police on Thursday evening.

'He's been charged with assault, three counts of assault, and one count of criminal mischief,' said Thomas Antonetti of the NYPD. 'He's still in custody, still at the police precinct until he's removed to court this morning.'

Antonetti added 25-year-old Cian Cowley, also a mixed martial arts (MMA) fighter, from Hyde Park, Dalkey, has been charged with assault.

McGregor is not an American citizen and thus could possibly be denied entry into the country if convicted of the charges.

Conor McGregor is seen in new footage at a UFC 223 media day at Barclays Center in Brooklyn

The dolly hits the window, which smashes, sending glass flying over the passengers inside

The incident, which led to some injuries and the cancellation of several fights, unfolded on Thursday as the UFC held a press conference for Saturday's fight card at Barclays Center in Brooklyn. McGregor and his entourage entered through a side entrance and attacked a van containing a group of other fighters.

Lightweight Khabib Nurmagomedov was in the van and may have been the target of the McGregor's rage. The 29-year-old Russian recently had a public confrontation with Artem Lobov, a friend and training partner of McGregor's who was scratched from his own fight on Saturday because of his involvement in Thursday's incident.

The footage shows McGregor approaching the bus as it inched towards the truck elevators to exit the building. At one point he can be seen running for a dolly before picking it up and throwing it at the moving vehicle, breaking a window through which passengers can be seen.

The incident took place at the Barclay's Center in Brooklyn, ahead of Saturday's UFC 223

McGregor was held at the 78th precinct, which sits across the street from Barclays Center

'Approximately 20 guys were apparently let in through the doors by the Mac Life guys, who were credentialed here,' UFC president Dana White explained, referencing McGregor's brand and its employees who allegedly helped the Dublin native and his crew enter Barclays Center.

'They opened the doors for them, through an entrance, they stormed the building, got down to the loading docks where the fighters were getting on the buses and started to attack the buses, throwing trash cans and dollies and things like that,' White continued. 'Broke one of the windows and cut Michael Chiesa real bad. He cut his head and cut his face.

'[UFC fighter] Rose Namajunas was apparently almost hit. She's super upset right now... Hurt one of our employees, broke one of our employee's knuckles.'

Footage from the scene shows McGregor attempting to hurl a guard rail through the window of the van full of fighters before being prevented by security.

The Dubliner can then be seen trying to do the same with a trash can before being thwarted once again.

Conor McGregor and his team crashed the UFC 223 media day at Barclays Center looking for Khabib Nurmagomedov, who is slated to fight Max Holloway on Saturday

After failing to find Khabib Nurmagomedov on the main concourse, McGregor went downstairs to the event level, where the MMA fighter was boarding a van at the truck elevator

McGregor attempted to grab a guard rail and use it to smash the bus before he was restrained

The confrontation led to several injuries and the cancellation of three of Saturday's scheduled bouts.

Lightweight Michael Chiesa suffered a laceration to his face and, as a result, was forced to pull from Saturday's event, the UFC announced Thursday evening.

Chiesa tweeted to say the New York State Athletic Commission had decided to remove him from his bout against Anthony Pettis.

Addressing his opponent, the 30-year-old Colorado native said: 'I'm devastated to say the least. @Showtimepettis I hope to run this match up ASAP, June 9th in your backyard. That's all I have to say for now. Much love.'

Flyweight Ray Borg was also scratched ahead of his bout with Brandon Moreno due to 'multiple corneal abrasions', the UFC said in a statement.

And because the featherweight Lobov was involved in instigating the fracas, his bout with Alex Caceres was also cancelled.

Making matters worse for the UFC, Max Holloway was not medically cleared to fight Nurmagomedov in the main event. Now another fighter will be needed to step in on extremely short notice or the main event will be cancelled.

Chiesa wrote the New York State Athletic Commission scratched him from Saturday's fight

Rose Namajunas (left) was on the bus and left shaken after the attack while Michael Chiesa was left with a laceration to his face after a chair was thrown through one of the van's windows

Police and EMS were called to the scene according to White who described the event as 'the most disgusting thing that ever happened in the history' of the UFC.

McGregor was scheduled to lose his UFC lightweight belt on Saturday to the winner of the title bout between Max Holloway and Nurmagomedov - a contest that is now up in the air because Holloway was not medically cleared to fight Saturday.

I am laughing inside. You [McGregor] broke window? Why? Come inside. If you real gangster why don’t you come inside? This is big history gangster place. Brooklyn. You want to talk to me? Send me location. I am going to come. No problem. Khabib Nurmagomedov

White previously ruled that McGregor, the first UFC fighter to hold two world titles simultaneously, would have to forfeit the lightweight belt to whomever won that fight because the Irishman has not participated in a UFC event since 2016 - nearly a year before his doomed boxing debut against Floyd Mayweather Jr. in August of 2017.

McGregor gave a clumsy reaction to White's decision on Twitter: 'You's'll strip me of nothing you's do nothing c****.'

MMA reporter Ariel Helwani caught up with Nurmagomedov, who said that he is 'laughing inside.'

'You broke window?' he asked rhetorically. 'Why? Come inside. If you real gangster why don’t you come inside? This is big history gangster place. Brooklyn. You want to talk to me? Send me location. I am going to come. No problem.'

Khabib Nurmagomedov was reportedly the target of Conor McGregor's agitation on Thursday

Nurmagomedov, a front-runner to be McGregor's next opponent, had a run-in with Artem Lobov (pictured) earlier this week, threatening him if he ever spoke his name again. Lobov is a friend and training partner of McGregor's and it's likely that the incident was a response to this

McGregor took issue with being stripped of his belt by White and the UFC

Nurmagomedov, a front-runner to be McGregor's next opponent, had a run-in with Lobov earlier this week, threatening him if he ever spoke his name again.

'Never say my name,' Nurmagomedov said in a clip that was later posted to YouTube. 'You got me? I didn't hear you, motherf*****.'

Lobov is a long-time friend and training partner of McGregor's and it is likely Thursday's incident was a response to this altercation.

He has been pulled from UFC 223 as a result of the incident.

'Artem was [in the group of people involved],' White said. 'Artem's off the card. That fight's not happening.'

The winner of Saturday's bout seemed likely to be among the top contenders for the next big-money fight with McGregor, although all of that appears up in the air now.

White previously said McGregor, UFC's biggest box office attraction, would fight this year.

Now, though, White says he doesn't want anything to do with McGregor.

'Right now, absolutely not,' White said, as quoted by ESPN. 'Do you want to be in business with Conor McGregor right now? Do you want to chase this guy for interviews and buy his fights? I don't think anybody is going to want to right now.

'I don't know if he's on drugs or what his deal is, but to come and do this and act like this? You're talking about a guy who has a baby. He just had a kid.'

Nurmagomedov was the only fighter in New York who skipped the open workout and instead turned the session into a Q&A with fans. He tossed T-shirts to fans asking the best questions and posed for a selfie with a kid in a papakha.

One fan shouted if he would call out McGregor after the fight.

'We're going to make him a little bit humble,' Nurmagomedov said.

Nurmagomedov, a front-runner to be McGregor's next opponent, had a run-in with Artem Lobov earlier this week, threatening the Irishman's friend and training partner if he ever spoke his name again. 'Never say my name,' Nurmagomedov said in a clip that was later posted to YouTube. 'You got me? I didn't hear you, motherf*****'