Afghan President Hamid Karzai has warned a booming trade in opium and heroin threatens the existence of Afghanistan as a nation-state.

In an interview with the Associated Press Sunday, the Afghan leader called drugs a bigger threat than terrorism. He said foreign crime groups and terrorists are forcing farmers to grow poppies. He said drugs are criminalizing the economy, tainting the country's image and hindering the development of strong government institutions.

During the interview, Mr. Karzai also invited Taleban leader Mullah Omar to contact his government and seek reconciliation. But he expressed doubts that the fugitive leader would come out of hiding.

The Afghan leader also said that NATO-led troops taking over security in southern part of the country must not use aggressive tactics without government permission.

Some information for this report provided by AP.