One accused him of misunderstanding the advice he had been given on the issue at a Downing Street summit.

Black community leaders reacted after Mr Blair said the recent violence should not be treated as part of a general crime wave, but as specific to black youth. He said people had to drop their political correctness and recognise that the violence would not be stopped "by pretending it is not young black kids doing it".

It needed to be addressed by a tailored counter-attack in the same way as football hooliganism was reined in by producing measures aimed at the specific problem, rather than general lawlessness.

Mr Blair's remarks are at odds with those of the Home Office minister Lady Scotland, who told the home affairs select committee last month that the disproportionate number of black youths in the criminal justice system was a function of their disproportionate poverty, and not to do with a distinctive black culture.

Giving the Callaghan lecture in Cardiff, the prime minister admitted he had been "lurching into total frankness" in the final weeks of his premiership. He called on black people to lead the fight against knife crime. He said that "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".

Mr Blair said he had been moved to make his controversial remarks after speaking to a black pastor of a London church at a Downing Street knife crime summit, who said: "When are we going to start saying this is a problem amongst a section of the black community and not, for reasons of political correctness, pretend that this is nothing to do with it?" Mr Blair said there needed to be an "intense police focus" on the minority of young black Britons behind the gun and knife attacks. The laws on knife and gun gangs needed to be toughened and the ringleaders "taken out of circulation".

Last night, British African-Caribbean figures leading the fight against gang culture condemned Mr Blair's speech. The Rev Nims Obunge, chief executive of the Peace Alliance, one of the main organisations working against gang crime, denounced the prime minister.

Mr Obunge, who attended the Downing Street summit chaired by Mr Blair in February, said he had been cited by the prime minister: "He makes it look like I said it's the black community doing it. What I said is it's making the black community more vulnerable and they need more support and funding for the work they're doing. ... He has taken what I said out of context. We came for support and he has failed and has come back with more police powers to use against our black children."

Keith Jarrett, chair of the National Black Police Association, whose members work with vulnerable youngsters, said: "Social deprivation and delinquency go hand in hand and we need to tackle both. It is curious that the prime minister does not mention deprivation in his speech."

Lee Jasper, adviser on policing to London's mayor, said: "For years we have said this is an issue the black community has to deal with. The PM is spectacularly ill-informed if he thinks otherwise.

"Every home secretary from [David] Blunkett onwards has been pressed on tackling the growing phenomenon of gun and gang crime in deprived black communities, and government has failed to respond to what has been a clear demand for additional resources to tackle youth alienation and disaffection".

The Home Office has already announced it is looking at the possibility of banning membership of gangs, tougher enforcement of the supposed mandatory five-year sentences for possession of illegal firearms, and lowering the age from 21 to 18 for this mandatory sentence.

Answering questions later Mr Blair said: "Economic inequality is a factor and we should deal with that, but I don't think it's the thing that is producing the most violent expression of this social alienation.

"I think that is to do with the fact that particular youngsters are being brought up in a setting that has no rules, no discipline, no proper framework around them."

Some people working with children knew at the age of five whether they were going to be in "real trouble" later, he said.

Mr Blair is known to believe the tendency for many black boys to be raised in families without a father leads to a lack of appropriate role models.

He said: "We need to stop thinking of this as a society that has gone wrong - it has not - but of specific groups that for specific reasons have gone outside of the proper lines of respect and good conduct towards others and need by specific measures to be brought back into the fold."

The Commission for Racial Equality broadly backed Mr Blair, saying people "shouldn't be afraid to talk about this issue for fear of sounding prejudiced".

Mr Blair spoke out as a second teenager was due to appear in court charged with the murder of 14-year-old Paul Erhahon, stabbed to death in east London on Friday. He was the seventh Londoner under 16 to be murdered since the end of January, and his 15-year-old friend, who was also stabbed, remains in hospital.