LONDON (Reuters) - British police said on Monday they had charged five people over a “brutal” attack involving a gang of up to 30 assailants on a teenage asylum seeker in south London which left the victim with a fractured skull and blood clot on his brain.

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Detectives, who are treating the incident as a racially motivated hate crime, said the 17-year-old Kurdish Iranian boy was left critically injured after the attack shortly before midnight on Friday as he waited at a bus stop with two friends near a pub in Croydon.

“It is understood that the suspects asked the victim where he was from and when they established that he was an asylum seeker they chased him and launched a brutal attack,” said Detective Inspector Gary Castle.

“He sustained serious head and facial injuries as a result of this attack, which included repeated blows to the head by a large group of attackers.”

The teenager is recovering in hospital and is now in a serious but stable condition which is not believed to be life-threatening, police said. Officers said they had made 11 arrests since Friday night and charged five people, three aged 20 and two aged 24, with violent disorder.

One man was also charged with racially aggravated grievous bodily harm and they are all due to appear in court later on Monday. Three others, arrested on suspicion of attempted murder and violent disorder, remain in custody.

Detective Superintendent Jane Corrigan said as many as 30 people were involved in the apparently motiveless attack and the teenager was lucky not have been killed.

Immigration has been a major political issue in Britain and was one of the factors that swayed voters to back leaving the European Union in last year’s referendum in order to have more control on the numbers coming to the country. The Brexit vote also led to a spike in hate crimes.

“I haven’t seen an attack like this in a number of years and certainly nothing in London,” she told Sky News. “This was just appalling. The level of violence used was just unnecessary and just shows a real hatred with those involved.”

In a tweet after the attack local lawmaker Gavin Barwell described those responsible as “scum” while London Mayor Sadiq Khan vowed the perpetrators would be brought to justice.