AI in a Thursday report said it visited holding centers in Libya housing "thousands" of foreign nationals, which the organization said were detained "solely for immigration purposes."
The report said most of the refugees were held without access to medical care or were otherwise subjected to ill-treatment or torture.
"The torture and ill-treatment we uncovered at holding centers is unacceptable and is a stain on the record of post-Gadhafi Libya," he said in a statement.
The U.N. Support Mission in Libya said many of the country's post-war political and national security challenges were the likely result of "decades of authoritarian rule."
Libya's post-war progress has been slowed by internal rivalries. The government was accused of caving into the demands of armed groups who seized control of several official buildings last month.
"Libya's government must show the world it is serious about protecting the rights of all individuals in Libya, whatever their status and nationality," Sahraoui said.