Criminal gangs are infiltrating schools in England and sometimes using primary-age children to run messages between members, a minister has warned.
It is feared gangs are recruiting pupils in schools
The Schools Minister, Jim Knight, said the problem existed in four cities but later said London was the main problem.
He told the Commons education select committee he wanted to tackle it before it became "a genuine worry".
Mr Knight also said schools should debate the race row which erupted around Channel 4's Big Brother show.
He told the cross-party committee of MPs that he accepted his department was "going to set hares running in the media" on the issue of criminal gangs, "but we have to be open about it".
"It is an emerging issue that we want to nip in the bud now before it becomes something that is a genuine worry for parents and pupils," he said.
Mr Knight said there were about 10 gangs active in Birmingham, and many more in London.
Birmingham City Council's children's director, Tony Howell, said was aware that gangs in cities in England did attract loyalty from young people in schools.
"Quite often young people's identification with gangs does not go any further than just this," he said.
"Any evidence of criminal or unacceptable behaviour in schools is referred to the police."
Mr Knight had also mentioned Manchester, and said there was a problem with "a couple" of gangs active in schools in Nottingham, too, but later retracted this.
A spokesman for Nottinghamshire Police said the force had encountered nothing to suggest city schools were being used as recruiting grounds for established drugs gangs.
Manchester's director of children's services, Pauline Newman, said head teachers had not raised it as an issue with her, and she would be requesting details from the minister about the information he had.
Mr Knight said a particular concern was that very young children in a very few primary schools were being used to "run" messages between older gang members, often siblings.
He said police were using intelligence on street gangs to help schools tackle the problem.
The issue was being dealt with effectively in the London boroughs of Southwark and Haringey, he said.
"It's a relationship with criminal gangs outside school that is starting to come in[to] school just in those four places that we want to be able to help schools to do something about."
Mr Knight said he was not aware of pupils being forced to take or sell drugs.
The Department for Education and Skills says an estimated 100 to 200 organised criminal gangs are active in London.
But a spokesman said there were no figures for the number of gangs which had infiltrated schools in the capital.
Mick Brookes, general secretary of the National Association of Head Teachers, said heads were well aware that organised criminal gangs were infiltrating schools.
He said schools must remain a "haven of safety and security" for young people.
Big Brother row
Mr Knight said the row over whether Jade Goody and fellow Big Brother housemates racially bullied Indian actress Shilpa Shetty had got a national debate going and young people should join in.
Goody said her comments were a big mistake
Mr Knight said bullying "should not be tolerated in any form", whether it be racist, homophobic or otherwise.
Asked specifically how he felt the bullying row over Big Brother would affect pupils, Mr Knight said the debate could help them to explore their own language and attitudes.
"We've got a debate going among young people about whether their language is racist," Mr Knight said.
"And I hope that's being discussed in schools up and down the country."