LONDON -- Authorities in London charged five people Monday in an unprovoked attack on a 17-year-old Iranian-Kurdish asylum-seeker as police sought to piece together the mob violence that involved up to 30 people.

London’s Metropolitan Police say the five were charged with violent disorder, with one also being charged with racially aggravated grievous bodily harm following the attack Friday in the London borough of Croydon. Three others remain in custody.

Police said a group of youths approached the teen at a bus stop and questioned him. Upon learning he was an asylum-seeker, they chased him through the streets and beat him. The attack only stopped after police sirens could be heard and bystanders intervened. The teen’s two other friends got away.

The teen has been hospitalized with a fractured skull and a blood clot on the brain but police say he is starting to make a recovery and may be moved Monday out of intensive care.

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Detectives are trying to find the victim’s family, who live in Iran. He has not been named.

As the investigation has progressed, police have increased their estimates of the number of people involved in the highly unusual incident.

“I think this was probably confidence by numbers,” Detective Superintendent Jane Corrigan said. “It started off with this smaller group of people, who were joined by between 20 to 30, and they just viciously attacked these individuals because they were asylum-seekers.”

The five people arrested by police are: Daryl Davis, 20, Danyelle Davis, 24, Barry Potts, 20, George Walder, 20, and Jack Walder, 24. All are from Croydon and have been charged with violent disorder.

George Walder has been additionally charged with racially aggravated grievous bodily harm.

Political leaders have condemned the attack, with Conservative Party lawmaker Gavin Barwell describing the attackers as “scum.”

London Mayor Sadiq Khan condemned the attack, which he said “has no place in London, Britain or anywhere else,” and vowed the attackers would be brought to justice.

In the aftermath of the June 2016 vote to leave the European Union, Britain saw a surge in xenophobia expressed in taunts, threats and worse. For many, foreign- and native-born, the U.K. suddenly became a much scarier place.

“Before Friday we lived in a tolerant society,” Oana Gorcea, a 32-year-old Romanian who had been in Britain since she was a teenager, said last year in the wake of the vote. “I’ve been here 13 years, but I’ve never felt like I had to hide where I came from. But from Friday, things completely changed.”

Much of western Europe has seen a rise in xenophobic crime and rhetoric in recent years, as far-right political groups seize upon fears over the influx of many thousands of refugees and migrants from war- and poverty-plagued nations in the Middle East and north Africa.