Armed militia groups in Libya that formed along tribal lines after the ouster of the Moammar Gadhafi regime have turned on one another and now rule most of the country, torturing their opponents with impunity, Amnesty International says.

It's not just the revenge attacks or tribe-on-tribe feuding, but the gross human rights abuses that go unchallenged by Libya's new government, CBC's David Common reports from New York.

When Amnesty International investigators visited detention facilities, inmates told of rape by guards and beatings for hours with whips, cables, metal chains, wooden sticks and electric shocks with live wires, Common reported.

Militia members didn't bother stopping one beating even when Amnesty's team arrived, saying inmates who had been ordered released would not be.

At least 12 detainees have died since September after torture, Amnesty said in a report released Wednesday evening.

"Their bodies were covered in bruises, wounds and cuts and some had had nails pulled off," the group said.

"There's torture, extrajudicial executions, rape of both men and women," Navi Pillay, the United Nations high commissioner for human rights, said on Jan. 27.

The Amnesty International report is a fresh blow to Libya's new government, the National Transitional Council, which helped lead the anti-Gadhafi uprising that broke out one year ago this week and became a brutal, eight-month civil war.

Brigades not reined in

Since the war's end with the capture and killing of Gadhafi last October, the NTC has struggled to extend its control over the vast desert nation.

It has largely failed to rein in the hundreds of brigades that fought in the war, many of which now run their own detention centres for those accused of links to Gadhafi's regime.

"Nobody is holding these militias responsible," Donatella Rovera, senior crisis response adviser at Amnesty International, told The Associated Press by telephone from Jordan on Wednesday, a day after she left Libya.

The humanitarian group Doctors Without Borders suspended its work in prisons in Misrata in late January because it said torture was so rampant that some detainees were brought for care only to make them fit for further interrogation and abuse.

Rovera accused the Tripoli-based national government of lacking political will.

"They're not willing to recognize the scale of the problem. It is way, way beyond individual cases. It's an irresponsible attitude," she said.

With files from The Associated Press