AFGHANISTAN'S chief prosecutor has thrown down a gauntlet to Hamid Karzai by announcing an unprecedented attempt to prosecute for corruption two sitting cabinet members who cannot be touched until the president strips them of their ministerial immunity.

Mohammad Ishaq Aloko, the attorney general, said he was preparing a case for the prosecution of two members of Karzai's current cabinet as well as three former ministers, in what could become a key test of the Afghan president's willingness to tackle corruption. The two ministers have not been named, but speculation has focused on the minister of mines and the minister of religious affairs.

Fazel Ahmad Faqiryar, the deputy attorney general, said they had collected sufficient evidence to prosecute officials at the ministry but not the minister, Sadiq Chakar, although the investigation was continuing.

The officials allegedly overcharged for rented accommodation in Makkah to house Afghans during the annual hajj pilgrimage and pocketed the difference. They were discovered on their return from Saudi Arabia with $360,000 on them.

On Sunday, Chakar angrily denied local media reports that he was being investigated and said he was the victim of a plot to smear him. Mohammad Ibrahim Adel, the minister of mines, refused to comment.

Afghanistan has vast, untapped mineral wealth and the ministry of mines is responsible for issuing large numbers of short-term excavation rights. Irregularities have been alleged in the issuing of a $2.9bn contract to a Chinese conglomerate to exploit the Aynak copper reserve south of Kabul - one of the world's biggest copper stores.

The Washington Post recently reported allegations by US officials that Adel had taken a $30m bribe from the Metallurgical Corporation of China to secure the deal. He denied receiving any illicit payments.

The attorney general is looking at around 40 cases, with senior officials in the “high single figures”, an official said. But under Afghan law ministers and governors cannot be investigated and must be suspended from their duties. “It's a great thing that the Afghans are finally publicising cases like this, but at the moment they have no power to bring these people in,” said one western lawyer in Kabul.

Adding to the frustration of international anti-corruption officials, the country's 2005 constitution calls for special courts to be set up to hear cases against various types of officials. It is hoped that the supreme court will back the establishment of a specialised anti-corruption tribunal with secure facilities to protect the judges to hear all such cases. But no site has yet been identified.

Much international effort has gone into improving Afghanistan's law enforcement agencies, with British lawyers helping to mentor prosecutors in a special unit of the attorney general's office focused on high- level corruption. Also recently set up is the Serious Crimes Task Force (SCTF), known as the “Afghan FBI” because the elite police operatives are trained by the FBI and the UK's Serious Organised Crime Agency (Soca) to use wiretaps and other sophisticated methods to collect evidence.

— The Guardian, London