The accusations cast more doubt on government claims to have overhauled police practices since an independent inquiry found systematic human rights abuses during a crackdown on anti-government protests last year. More than 80 people have been killed in the 17-month uprising.
The Bahraini regime had previously denied that the black sites existed, despite persistent allegations that beatings and torture had continued unabated since the report was published in November. But officials now admit privately that some police officers have continued to operate outside the law.
Opposition groups claim that a youth centre just outside the capital, Manama, and a police equestrian centre in the western district of Budaiya, have been used to beat and interrogate detainees before they are transferred to police stations, where stricter procedures are now in place. Cameras have now been installed outside the two sites, identified in testimony to human rights groups, to monitor those going in and out.