Libya's regular army and array of militias have been torturing loyalists of slain dictator Muammar Gaddafi, several of whom have been killed in custody, human rights groups have charged.
Amnesty International said that despite promises, Libya's new rulers have made "no progress to stop the use of torture", as Doctors Without Borders suspended its work in the third-largest city Misrata over similar claims.
Their accusations come after a top UN official raised concerns that militias composed of former rebels who helped topple Gaddafi were posing an increasing security risk as they repeatedly clashed with each other.
"Several detainees have died after being subjected to torture in Libya in recent weeks and months amid widespread torture and ill-treatment of suspected pro-Gaddafi fighters and loyalists," London-based Amnesty said in a statement.
It said its delegates met detainees held in Tripoli, in Misrata and in smaller towns such as Ghariyan who showed visible signs of torture inflicted in recent days and weeks.
"The torture is being carried out by officially recognised military and security entities, as well by a multitude of armed militias operating outside any legal framework," it said.
Donatella Rouvera, senior adviser at Amnesty, said in the statement that it was "horrifying to find that there has been no progress to stop the use of torture".
"We are not aware of any proper investigations into cases of torture," she said.
Detainees told Amnesty they had been beaten for hours with whips, cables, plastic hoses, metal chains, bars, wooden sticks and given electric shocks with live wires.
The watchdog said the detainees, both Libyans and foreigners from sub-Saharan Africa, were tortured soon after they were seized by militias in officially recognised detention centres in places like Misrata.
Misrata withstood a devastating siege by Gaddafi's forces during last year's uprising. Its fighters later unleashed a fierce attack on the dictator's hometown of Sirte, where he was killed on October 20.
"Several detainees have died in the custody of armed militias in and around Tripoli and Misrata in circumstances that suggest torture," Amnesty added.
Rouvera said the issue was aggravated as the police and judiciary remained "dysfunctional" cross Libya.
Libyan Justice Minister Ali H'mida Ashur neither confirmed nor denied the allegations, but told AFP that "when such complaints reach the general prosecutor or the military prosecutor, necessary action will be taken."
He said the authorities have set up a committee to monitor jails across the country and acknowledged that some prisons were under the control of militias.