The UN Secretary General, Antonio Guterres, has called on the "Libyan government" to bring all prisons under its control and free them from the grip of militias, adding that some of those militias are running migrant-smuggling networks in the country.

Guterres said in a report to the Security Council released Thursday that torture and arbitrary detention is widespread in Libya.

"About 6,400 detainees are held in 26 official prisons but thousands of others are being held in facilities with little government control or directly run by armed groups." The report indicated.

Guterres says he remains deeply concerned about widespread human rights violations and abuses committed in the context of detention and the prolonged arbitrary detention of thousands of men, women and children without due process.

"The government must protect detainees against torture and all prisons must be under effective government control and free of any influence or interference of armed groups," he added.

Guterres also explained that there had been an increase in the number of migrants and refugees who were detained over the past 6 months.

"About 5,300 refugees and migrants have been detained in Libya of whom 3,700 were in need of international protection. In all, there are over 669,000 migrants in Libya, of whom women and children make up 21 percent," according to the report.