 In 2010 around 520 Sahrawi civilians remained "disappeared" by Moroccan forces, according to human rights groups; some estimate that the total number of "disappeared" could be as high as 1,500.In the past, Morocco denied that any such political prisoners existed, but in 1991 released nearly 200 "disappeared" prisoners, many of whom had been held in secret detention centers since the mid-1970s.Since then, there have been no further releases of "disappeared" prisoners.