LONDON (AP) — UK police have arrested six people in a vicious attack on a teenage asylum-seeker in the London borough of Croydon.

Authorities are questioning four men and two women, all in their 20s, on charges of attempted murder in the attack that left a 17-year old Kurdish-Iranian hospitalized with a fractured skull and a blood clot on his brain.

Police say eight youths approached the teen at a bus stop Friday night. Upon learning he was an asylum-seeker, they chased him through the streets and beat him. The attack only stopped after bystanders intervened and police sirens could be heard.

Police are treating the attack as a hate crime.

Britain has seen a surge in xenophobia expressed in threats, taunts and attacks after Britain's vote to leave the European Union.