(Reuters) - Nigeria launched a crackdown on informal Islamic schools and rehabilitation centers in late September after a man was refused permission to see his nephews at one institution and complained to police. Nearly 1,500 people have been freed so far.

Nigeria group Muslim Rights Concern estimates about 10 million children attend Islamic institutions in the West African country, which has a mainly Christian, relatively prosperous, south and a largely Muslim north with higher levels of child mortality and malnutrition.

Below is a timeline of events since the crackdown started:

Sept. 26, 2019 - More than 300 boys and men, some as young as five, were rescued in a raid on a building that purported to be an Islamic school in northwestern Nigeria’s Kaduna city. Many were in chains and bore scars from beatings. Some had been there for years.

Oct. 14, 2019 - Police rescued 67 men and boys aged seven to 40 from an Islamic school in the town of Daura in northwestern Katsina state, where the captives had been shackled. Former students said instructors had beaten and raped inmates.

Oct. 16, 2019 - Police freed about 500 men and boys, many of whom had been chained to walls, molested and beaten, from an Islamic school in the northwestern city of Katsina in its eponymous state, law enforcement sources said.

Oct. 19, 2019 - Police freed nearly 150 students from a reformatory school Kaduna. At least 22 of the 147 released captives were female. Many of those freed had scars from abuse.

Oct. 24, 2019 - Police rescued 108 malnourished and sick captives aged from six to 45 from a so-called Islamic reform center in Ilorin in central Nigeria’s Kwara state.

Nov. 4, 2019 - Nigerian police released 259 people held captive at an Islamic rehabilitation center in the southwestern city of Ibadan, saying some had been chained.