Detectives investigating the murder of a teenager in London have formally named the victim and made two arrests.

Alex Smith, 16, from Brent, north-west London, was stabbed multiple times in Munster Square, Camden, on Monday after being chased by a group of people.

Three young men were heard "screaming and laughing" as they pursued the victim with a machete, according to eyewitnesses.Mr Smith could be heard shouting "help me, help me, help me" before collapsing near the doorstep of a family home, one unnamed witness said.

He was pronounced dead at the scene after police were called at 11.10pm.A post-mortem carried out on Thursday found he died from a single stab wound to the chest.

A 23-year-old man and an 18-year-old man were arrested on Wednesday and remain in custody.

Detective Inspector Jamie Stevenson said: "We're still keeping an open mind concerning the motive of this brutal attack and thank those who have come forward and spoken to us so far.

"We know there are individuals out there who can assist this investigation and we continue to appeal for those people to make contact with officers.

"Please do the right thing and come forward, anonymously if need be, but do make the call."

The suspects made off in a vehicle that was discovered burnt out nearby, police said.

A man who lives near to where the body was found, who did not want to be named, said the square has recently become a hotspot for drug taking and groups of men regularly gather there.

Any witnesses or anyone with information is asked to call police on 020 8358 0400 quoting CAD8433/12Aug