One held a snarling pit bull terrier that strained against its leash. Chants of "Kill him!" erupted from the mob.

The teenagers, some of whom still wore their school uniforms, seized Yenga, and one stabbed him in the heart. Witnesses heard members of the gang laugh as he lay dying in his girlfriend's arms.

His death, while shocking, was not a rare event: Britain is reeling from a spate of knife attacks including 12 stabbing deaths - six involving the slaying of youths - in a single week this month.

Few have ready explanations for the trend, but parents and lawmakers alike fear an epidemic of violence among Britain's youth is putting all generations at risk.

"Too many people, young and old, do not feel safe in the streets, and sometimes even in their homes," Prime Minister Gordon Brown acknowledged, pledging tougher sentences for those carrying knives.

In a country where guns are scarce and account for only 11 percent of homicides, knives are used in around two-thirds of killings and, according to lawmakers, carried by increasing numbers of young people.

Nationwide statistics for knife crimes among youths are not available. But in London, the number of teenage murders, which held steady at under 20 per year between 2000 and 2006, rose to 26 last year and already stands at 19 for the first seven months of 2008 - the majority of them stabbing deaths.

The apparent surge in knife crime is set against Britain's unwanted record for the worst teenage pregnancy and juvenile drinking rates in Europe.

Chris Preddie, a 21-year-old former gang member whose brother was shot dead in a drug-related feud, said fear is driving children to seek weapons.

"It is about being afraid . . . and wanting to protect themselves," Preddie said.

Legislators have pledged $198 million to respond, promising to strip problem families of social housing, allow teachers more freedom to search children for weapons, and urge municipal leaders to impose curfews on teenagers in trouble spots.

Some experts say the problem of youth violence is exaggerated - part of a familiar pattern of demonizing teenagers similar to panics over biker gangs in the 1960s or mobs supposedly inspired by a movie version of the book A Clockwork Orange in the 1970s.

One recent knife slaying struck a particularly strong chord.

Ben Kinsella, the 16-year-old brother of a television soap actress, was stabbed to death in London on June 29 after he apparently attempted to intervene in a fight among fellow youths.

Hundreds laid flowers and held candles during a moonlight vigil in the London suburb where he was slain. Before his death, Kinsella had written a letter to Brown as part of a school project, warning of a rise in knife crime.

Yenga, weeks before he was fatally stabbed last year, had appeared in an MTV documentary on knife crime, and said he was growing worried about an increasingly violent atmosphere in the capital.

Jailing five teens in the killing, Judge Christopher Moss said Yenga's death was likely the result of a minor feud. It was the "needless loss of another young life" because of knives, he said.