Nigerian police say they rescued at least 150 students on Saturday from a purported school in the country's northern region, which claimed it was teaching them Islamic studies but had instead subjected them to abuse.

The rescue was the fourth such operation in a month and brings the total released from religious schools in northern Nigeria to more than 1,000.

The raid will put more pressure on President Muhammadu Buhari to take action on loosely regulated Islamic schools called Almajiris, which experts say teach millions of children across the mainly Muslim north of the country.

Kaduna state governor Nasir El Rufai ordered the raid on the Islamic reform school in Rigasa, officials said. The captives were gathered later at a camp nearby, standing in lines in maroon uniforms as state officials tended to them.

Unlike the other schools, at least 22 of the 147 released captives were female, according to Hafsat Baba, Kaduna's commissioner for human services.

The condition of those released was not immediately clear.

An official told Reuters the school was owned by the same man who owned one of the schools raided in neighboring Katsina state earlier this week and had already been arrested by police.

Those freed from other schools over the past month – including two this week – were chained on walls, beaten and sexually molested.

At the other raided facilities, some parents thought their children would be educated and even paid tuition. Other families sent misbehaving or difficult family members and wards to them for discipline.