Southern provinces are the source of most Afghan poppy production

It called on the government to stop powerful individuals undermining the justice system through bribes, corruption and threats.

Afghanistan supplies more than 90% of the world's illicit opium, the main ingredient of heroin.

The UN body says its cultivation has reached unprecedented levels.

Illegal trade

Christina Oguz, director of the UN Office on Drugs and Crime in Afghanistan, said drug traffickers and corrupt government officials operate with impunity in the country.

"Powerful individuals are able to compromise the justice system through bribes and corruption, as well as implicit and explicit threats," she said.

"Such situations can no longer be tolerated if Afghans are to have the type of judicial system and functioning institutional structures that they deserve."

Afghanistan grows nearly all of the world's opium poppy crop in an illegal trade worth billions of dollars.

A recent US State Department report said poppy cultivation helps Taleban insurgents obtain money and weapons.

The drug trade hinders progress towards economic stability and democracy, the report said.

The growth in Afghanistan's opium crop began in earnest after the overthrow of the Taleban by US-led and Afghan forces in 2001.