Libya's regular army and array of militias have been torturing loyalists of slain dictator Moamer Kadhafi, several of whom have been killed in custody, human rights groups charged on Thursday.

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 Kadhafi 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-Kadhafi 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 recognized 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 recognized detention centres in places like Misrata.

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