A headteacher has advised some parents to keep their children away from school for their own safety because of violence supposedly sparked by the cartoons of the prophet Mohammed.
Parents with children at Bethnal Green technology college in London said fighting in the playground and outside the school gates has escalated over the past four weeks.
They say that groups of Asian youths, many of whom are not pupils at the school, have been waiting outside to pick fights with black, white and Turkish students.
Keith Holt, the headteacher, sent home several pupils last week with a letter which read: "Dear parent, as you know there have been incidents between some of our Year 10 and 11 boys in school and on the way home troublemakers not known to the school have been involved. I ask you to keep (your child) at home tomorrow and to telephone the school to arrange a meeting."
Linda David, a learning mentor, said her 15-year-old son had not worried about his safety until last month and that she had since caught him carrying a knife for self-defence.
She said the rows over the Danish cartoons of the prophet Mohammed were being used as an excuse by some pupils for the fighting.
The school, most of whose pupils are from Bangladeshi backgrounds, has refused to comment on the incidents.
But since the violence was reported by the Hackney Gazette last week, the school has held meetings with parents and police.
Tower Hamlets council said there was "no question of gang warfare", a comment backed by local police.
"Like most schools there are occasional incidents between individuals which are dealt with according to the school's usual disciplinary procedure," a council spokeswoman said.
However, Louise Alexander, a local Liberal Democrat councillor, said there had been a noticeable increase in fighting outside of school.
She said that campaigning by local Muslim anti-democracy groups could have been one of the contributing factors, but stressed that other matters may have had a greater effect on pupils' behaviour, including that the technology college was in special measures and had recently taken on 50 Turkish pupils from a closing school.