A Muslim free school has been told it must take "swift action" to address concerns over the way it is run or face the prospect of closure.
Al-Madinah Free School in Derby has failed to keep pupils safe, provide a good education and has discriminated against female staff, according to a letter sent to the school by Lord Nash.
The Schools Minister said that the school had "manifestly breached" its conditions, and can expect to be closed down if it does not make immediate changes.
Al-Madinah School, which is run by the Al-Madinah Education Trust, has been told it must provide evidence within the next week that it has stopped any practices that lead to women and girls being treated "less favourably" than men and boys.
It also has to notify all staff that they are not required to cover their hair if it is against their religion or beliefs.
According to a post on its website, the school has now reopened. A statement says the school has "now fully addressed the urgent Health and Safety issues that emerged. While it was regrettable that the school had to close at all, the well-being of our pupils will always be our first concern.
"Unsurprisingly, there has been a number of rumours circulating. While unfortunate, my decision to close the school related to a short-term Health and Safety issue that has now been completely resolved and will not reoccur.
"Our closure was not the result of our Ofsted Inspection Team deciding to close Al-Madinah School, now or in the future. At this point we would like to pass on our sincere thanks to our pupils, parents and other members of our community for their patience. With your continued support, Al-Madinah School will continue on its journey to realise its vision for the community we serve.
"Assuring you that we always have your children’s best interests at heart."
There have been reports that female teachers at the school - which claims a "strong Muslim ethos" - were forced to wear hijabs even if they were not Muslim.
Other reports claimed that girl pupils were made to sit at the back of the classroom and boys at the front.
Lord Nash's letter says: "The Trust has manifestly breached the conditions of its funding agreement by failing to ensure the safety of children at the school; delivering an unacceptably poor standard of education; discriminating in its policies and procedures towards female staff; and failing to discharge its duties and responsibilities in respect of the governing body.
"I will not tolerate breaches of the commitments you gave when entering into the funding agreement."
Lord Nash said he was writing to "underline the scale of my concerns" about the school.
"Unless swift action is taken to address these concerns in a comprehensive way I will be compelled to terminate the school's funding agreement," he warned.
Richy Thompson, of the British Humanist Association, told HuffPost UK he was concerned about the schools' freedom to depart from the national curriculum, as well as what he said was a lack of transparency over who is applying to open new institutions.
"They can teach pretty much what they like, in terms of RE and sex education," he said.
The school's founding headteacher Andrew Cutts-Mckay left after less than a year in post. He was quoted as saying, before the school opened, that it would "honour all faiths" and would have 50% non-Muslim pupils.
In a statement, Ofsted chief inspector Sir Michael Wilshaw said the school re-opened after inspectors made a return visit to ensure that the right checks - such as criminal records checks - were in place.
"Ofsted began an inspection of Al-Madinah School on Tuesday October 1," Sir Michael said.
"On the same day, the principal took the decision to close the school as a result of inspection concerns over safeguarding checks. Inspectors discovered that staff records showing whether they were cleared to supervise children were either missing or incomplete.
"The school remained closed until yesterday when inspectors made a return visit to satisfy themselves that the necessary safeguarding arrangements were in place and that there were sufficient numbers of adults with the necessary clearance for the school to function safely.
"In particular, inspectors needed to see evidence that CRB/DBS checks had been properly completed for employees and were held on an accurate, single central register."