A boy stabbed to death by a gang allegedly wielding knives and wide swords has been named by family friends as Hani Abou El-Kheir.

The 16-year-old was killed on Sunday night in Pimlico, London, with witnesses saying he screamed for his life.

Friend Mahmoud Abosiad visited the family and said: "He was a lovely boy. He did not deserve to end up on a slab."

Mohammed Alzubaidi, 49, from nearby Peabody Close, said his friend witnessed a gang of black and white teenagers carrying out the attack. "He said they were carrying knives, some of them with wide swords. He said the victim was screaming and trying to get away," Mr Alzubaidi said.

The fatally injured teenager was found by ambulance staff after emergency services were called to the Lupus Street area following reports that a youth had been stabbed. He was taken to a south London hospital where he died a few hours later.

A spokesman for the Metropolitan Police said: "A murder inquiry is now under way and an incident room will open in due course under detectives from the Specialist Crime and Operations Directorate. We must retain an open mind re the circumstances of the incident and any motive at this early stage."

The victim's mother, Pauline Hickey, who lives 100 yards from the murder scene, did not want to comment but an unidentified man at the family home said: "She's broken hearted." Evgeny Onegin, 22, whose third storey flat overlooks the crime scene said his flatmate saw the boy's attackers flee. He said: "My flatmate saw him bleeding out. He said he could see the wound bleeding out from all the way up here. He saw three or four guys running off up the street. Lots of people gathered quickly. The victim was shouting and people called an ambulance as they realised what happened."

Hani's name was flagged up to drugs workers on Wednesday, a Westminster Council drugs worker said. David Savizon, who works for the authority's Your Choice anti-gangs programme, said the boy's name came up at a local meeting as someone who was "on the periphery of having some sort of contact with gangs or activity such as drugs". He said: "He wasn't deemed significant in terms of being in a gang. He was mentioned as someone on the periphery." He added: "Unfortunately I wasn't able to meet him."

Mr Savizon, 34, who has 12 years of experience working with youngsters at risk of joining gangs, said the schoolboy would have been assessed before being approached by drugs workers. But he was not deemed to be a major concern, he said. "It was more of a bookmark just to see where this young person was," said Mr Savizon. "Everything I have heard about him, he was a very timid young man."

Mayor of London Boris Johnson said: "It is heartbreaking to see the life of another young Londoner taken so tragically. My thoughts are with this young man's family at such a terrible moment. This horrific incident serves as an unwelcome reminder that although violent crime in the capital continues to fall, we must continue our fight to tackle youth violence and get knives off our streets."