Tony Blair has called on black communities to denounce gun and knife crime, following the latest spate of youth-on-youth attacks.
The prime minister called for tougher action on gang crime in a speech in Cardiff, as he joined the Labour campaign trail in Wales.
Delivering a lecture in memory of former Labour prime minister James Callaghan, Mr Blair said people need to acknowledge a minority of black teenagers are responsible for most of the recent violence and these ringleaders need to be taken "out of circulation".
"We won't stop this by pretending it isn't young black kids doing it," Mr Blair said.
"The black community - the vast majority of whom in these communities are decent, law-abiding people horrified at what is happening - need to be mobilised in denunciation of this gang culture that is killing innocent young black kids."
The Liberal Democrats attacked his comments as "plain wrong and over simplistic". Party president Simon Hughes said many of the young people involved in gangs are white, mixed race or Asian, as well as black.
"Some of us live in the sorts of places where these attacks and tragedies happen and we know that the picture is much more complicated," he added.
Mr Hughes continued: "The common factor is that they either think weapons are cool or they're frightened and think it's necessary to defend themselves. All the evidence shows that young people are the most frequent victims as well as perpetrators of these horrendous crimes.
"The solutions are complex, but personal and family responsibility, appropriate education and training, lots of constructive activity and a major increase in qualified youth workers would make a massive difference."
However, the Conservatives welcomed Mr Blair's sentiment on gang crime but said it came too late and blamed Labour's policies for "soaring" violent crime levels.
"After ten years in power and just weeks before Tony Blair steps down, the public will wonder why it has taken so long for him to speak up," said shadow home secretary David Davis.
Labour has failed to tackle the causes of crime, Mr Davis claimed, warning Mr Blair that "he cannot put right in two months what he has got wrong in ten years".
After his lecture in Cardiff, Mr Blair joined assembly leader Rhodri Morgan on the campaign trail in Wales. Here, his presence was unusually welcomed by political rivals.
Both the Conservatives and Plaid Cymru quipped the prime minister is now so unpopular that he encourages voters to desert Welsh Labour.
"We are delighted that the Prime Minister is visiting Wales today," said the Conservative shadow Welsh minister Cheryl Gillan
She continued: "The more people he gets to meet the better. It will remind them of why after a decade of Labour it is so important to vote for change in May's assembly elections.
"Tony Blair and Rhodri Morgan's legacy in Wales will be one of failure and broken promises."
The Liberal Democrats echoed her claims, saying Tony Blair had not been a friend to Wales and his record three terms in power would be seen as years of missed opportunity.