The shocking scale of female genital mutilation (FGM) in a Swedish school, where every single girl in one class had been subjected to the procedure, has been revealed.

School health services in Norrköping, eastern Sweden, discovered 60 cases of FGM since March, according to the Norrköpings Tidningar newspaper.

In the class where all of the girls had FGM performed on them, 28 were subjected to infibulation - the most extreme kind where the clitoris and labia are complete cut away, and the genitals are sewn to leave a small vaginal opening.

Additional local services have since been provided to help the girls.

FGM is carried out for cultural, religious and social reasons within families and communities where it is believed to be a necessary preparation for adulthood and marriage.

Along with mental illnesses, the long-term physical consequences of FGM procedures can include chronic vaginal and pelvic infections, abnormal periods, persistent urine infections, possible kidney failure and infertility, according the NHS.

Performing FGM in Sweden has been an offence punishable by a prison sentence since 1982, but in 1999 the government extended the law to include procedures performed abroad.

"We're working to inform parents that they could face prison if they come back and their children have undergone female genital mutilation,” Petra Blom Andersson, student health coordinator in Norrköping, told the newspaper.

FGM is also a problem in the UK, where, it is estimated that over 20,000 girls under the age of 15 are at risk, and that 60,000 women have been operated on.

As is the case in Sweden, girls in the UK are most threatened during the summer months when they visit the countries from where their parents originate.