Detectives are questioning eight people over a suspected hate crime which left a teenage asylum seeker with a fractured skull and a blood clot on his brain.
The 17-year-old was attacked at a bus stop in Croydon, south-east London, on Friday by a gang of around eight people.
Neighbours claimed up to 20 people watched while he was kicked and beaten on the ground.
The incident has drawn widespread condemnation, with Tory minister Gavin Barwell describing the attackers as "scum".
Scotland Yard said a 23-year-old man was arrested in Croydon on Sunday on suspicion of attempted murder, while a 26-year-old man and 17-year-old girl were detained on suspicion of attempted murder and violent disorder.
Five other people are still being questioned by detectives while a sixth, a woman aged 20, was released without charge.
The group - three men aged 20, one aged 24 and a 24-year-old woman - are also being held on suspicion of attempted murder and violent disorder.
The teenager, a Kurdish Iranian, was waiting at a bus stop with two friends outside The Goat pub in the Shrublands area when the group approached them.
After discovering he was an asylum seeker they chased him and launched a vicious assault, repeatedly kicking him on the floor and aiming blows to his head.
The boy remains in hospital in a serious but stable condition, not believed to be life-threatening.
Police said around eight people were involved in the attack but residents said many more watched while the boy was beaten.
One resident of Shrublands Avenue told the Press Association: "There were more than eight people, there was a massive group coming up from The Goat pub.
"You couldn't see who was hitting who.
"There was one person, the one who ended up in hospital, he was getting absolutely beaten up - kicked, mostly in the facial area. He was getting kicked and punched by everyone.
"There was a group of roughly 10 people that was kicking and punching him, and the rest, another 10 or 20, were all just around watching.
"Then when they heard sirens they started to go. People that were there, witnesses, because they couldn't do anything against a group of 30 people, they had to wait until they moved off and that's when they managed to help him.
"That's eventually when the ambulance and police (arrived), and that was it."
Detectives are investigating whether some of those involved had been drinking in The Goat.
Managers at the pub said they were "saddened" to hear of the incident, adding: "We do not in any way condone such action and we will do anything within our powers to help police to bring those that carried out this act to book. To the victim, we pray for his speedy recovery."
Chief Superintendent Jeff Boothe, Croydon's borough commander, called it a "savage attack" and said it was only the intervention of passers-by and the arrival of police that stopped it being worse.
The "close-knit community" has been left shocked by the ferocity of the attack, he added, and extra officers have been out and about to reassure people.
He said: "This is not usual for the area, it is out of the norm. This is not Croydon, Croydon is a very diverse community - they celebrate their diversity."
Mr Boothe added: "Hate crime is something which we understand can be very, very divisive. Croydon is culturally diverse and we need to continue to celebrate that."
Mr Barwell, Croydon Central's MP, said: "I think most people in Croydon will be as appalled as I am that what appears to have happened is a young man who came to this country seeking sanctuary has apparently been targeted because of his ethnic background.
"It's an appalling crime and I hope the people responsible are caught quickly and receive the full force of British justice."
London mayor Sadiq Khan also condemned the attack, saying hate crime "has no place in London, Britain or anywhere else", while the Refugee Council said it was "disgusted" by the assault.
Labour leader Jeremy Corbyn also denounced it, saying: "Absolutely shocked at attack on young Kurdish asylum seeker, who came here searching for safety. I fervently hope he makes a full recovery."
Anyone with information about the attack should call police on 101 or Crimestoppers on 0800 555111.