Ali Ahmad Jalali has been one of the most powerful figures in President Hamid Karzai's government to speak out against the drug trade and the influence of warlords in Afghanistan.
Afghanistan supplies 87 per cent of the world's illegal raw opium, and accounts for almost all the heroin on the streets of London. British-led efforts to curb the opium trade have largely failed. The trade accounts for 60 per cent of Afghanistan's gross domestic product.
Mr Jalali said there were "various reasons" for his decision to resign, and that he wanted to return to academia. But he has been outspoken recently over the involvement of officials in the drug trade and is believed to have had differences with President Karzai over the appointment of provincial officials.
"I will not work as interior minister any more. Maybe there are reasons for this and maybe not but one of the main reasons is that I wish to resume my academic research," he said.
Mr Jalali is one of the most respected figures in President Karzai's government and his resignation will be seen as a setback.
Unlike many other senior ministers, who are warlords and their allies, Mr Jalali was a genuine technocrat. He said he will address a press conference today to explain the reasons for his resignation.Reuse content