An official investigation into torture in Afghan prisons has found widespread abuse, President Hamid Karzai says, following a UN report into the problem.

"According to the report of the commission of inquiry, half of the prisoners interviewed complained of mistreatment, harassment and even torture during their detention," the president's office said in a statement on Sunday.

It described prisoners' access to lawyers as "problematic", but made no conclusions or recommendations.

Karzai ordered the probe after the UN issued a damning report in January citing evidence of frequent abuse in the country's prison system.



Al Jazeera's Jennifer Glasse in Kabul

comments on the commission's findings

The report revealed that 326 of 635 prisoners interviewed across the country said they had been abused, including 80 minors.

Fourteen types of torture were described in the UN report, including beatings with cables and pipes, attacks on the genitals, threats of execution or rape, electric shocks and forced stress positions.

The UN also said 81 people imprisoned in southwestern Kandahar disappeared between September 2011 and October 2012.

"These findings seriously concern us," Jan Kubis, the UN special representative in Afghanistan, said at the time, calling on the government to "do more to prevent torture".

NATO forces in Afghanistan stopped sending prisoners to some Afghan jails after the reports of torture and asked Kabul to investigate allegations of abuse by members of a US-backed paramilitary police force.

Foreign combat troops are set to leave the country by the end of 2014 and hand over security to Afghan forces.