Britain's second city Birmingham launched a probe Monday into an alleged hardline Muslim plot to take control of schools.
The city council said it had appointed a chief adviser to examine at least 200 complaints as the investigation widened to 25 schools from an initial four.
Concerns about how some of the 430 schools in the central English city were being run first emerged last year in a leaked anonymous letter which outlined how to implement what it called Operation Trojan Horse.
The letter, which credited the alleged plot with forcing a change of leadership at four schools, gave instructions on ousting and replacing uncooperative headteachers and school governors.
"We have an obligation to our children to fulfil our roles and ensure these schools are run on Islamic principles," the letter says.
"We... are on our way to getting rid of more headteachers and taking over their schools."
The letter continued: "You must remember this is a 'jihad' and as such all means possible to win the war is acceptable."
Birmingham has a large Muslim population. Some 22 percent of the city's residents identified themselves as such in the 2011 census.
Since the letter emerged, whistleblowers including former staff have come forward, making claims that boys and girls were segregated in classrooms and assemblies, sex education was banned and non-Muslim staff were bullied.
In one case, it was alleged that the teachings of the firebrand Al-Qaeda-linked Muslim cleric Anwar al-Awlaki — who was killed by a US drone strike in Yemen in 2011 — were praised in an assembly.
"As more schools have come forward than the ones named in the Trojan Horse document, issues have arisen about behavior in schools, the way in which schools are run," city council leader Albert Bore told BBC television.
"It is about, generally speaking, the behavior of the schools, what happens within the schools, the school day, the school assembly, the way in which children in schools are organized."
The allegations focus on a category of schools known as academies. Established from 2000 onwards, they are state-funded but are self-governing and independent of local authority control.
Bore said it was "part of the frustration" that the city council had no remit in the schools, which answer to the national Department for Education.
"We do not know who's on the governing body (of the schools)," he said.
The council will publish its findings before mid-June.
Education Secretary Michael Gove has sent inspectors to 15 Birmingham schools in recent weeks.
On a visit to Birmingham earlier this month, Prime Minister David Cameron spoke about the issue, saying: "We will not accept any school begin run by extremists or promoting extremist views."
Deputy Prime Minister Nick Clegg said Monday that schools should not be allowed to become "silos of segregation."
"I am very concerned whenever I hear allegations that schools, funded by the taxpayer, become vehicles for the propagation of particular ideologies which divide young children and pupils off from other people in society," he said.
"The Department for Education is taking this very seriously."