A police officer has been filmed kicking and stamping on a man's head in an incident at Manchester Airport.
The officer, who was accompanied by two other taser-wielding officers, later struck another man on the back of the head.
More officers rushed to join the trio at Terminal 2, with onlookers shouting: "Oh, s**t."
The 44-second video, which circulated on social media this afternoon, raised serious questions about what sparked the incident.
An incident unfolded at Manchester Airport this afternoonTWITTERGreater Manchester Police later confirmed a female police officer sustained a broken nose as three officers were subject to a "violent assault".
In a statement, the force said: "Officers were called to reports of an altercation between members of the public in Terminal 2 at Manchester Airport.
"Whilst attempting to arrest one of the suspects of the earlier altercation, three officers were subject to violent assault, where they were punched to the ground.
"A female officer suffered a broken nose and all three were taken to hospital for treatment."
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Three officers were taken to hospital (stock pic)
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The statement added: "As the attending officers were firearms officers, there was a clear risk during this assault of their firearms being taken from them.
"Four men were arrested at the scene for affray and assault on emergency service workers.
"We acknowledge the concerns of the conduct within the video, and our Professional Standards Directorate are assessing this."
However, some social media users were left outraged by the conduct of officers.
The incident took place at Manchester Airport's Terminal 2
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One said: "It doesn't matter what happened prior to assaulting civilians who were at that time clearly not fighting."
The incident comes after an investigation was launched into Greater Manchester Police.
The force was found to have unlawfully arrested and stripped search several women.
Greater Manchester Mayor Andy Burnham commissioned Dame Vera Baird to interview 15 women and men who had complained about the force’s treatment.