KABUL (AFP) - An official investigation into torture in Afghan prisons has found widespread abuse, President Hamid Karzai said on Sunday, 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.

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

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

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 United Nations also said 81 people imprisoned in south-western 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".

Mr Karzai's spokesman Aimal Faizi questioned the motivations behind the UN report and said the government "is not involved in crimes against detainees".

He also said that torture and abuse of prisoners were "certainly not our policy", adding that the Red Cross had full access to Afghan detention centres and had not revealed any evidence of torture.