Western officials have called on President Karzai to act on corruption
Two Afghan cabinet ministers are under investigation for alleged corruption, the attorney general's office has said.
Deputy attorney general Fazel Ahmad Faqiryar told the BBC he could not name names but said a further 15 former ministers were also being investigated.
The Afghan government has been under intense Western pressure in recent weeks to do more to tackle corruption.
President Hamid Karzai promised at last week's inauguration to do more to end what he called a culture of impunity.
In his inaugural speech, he also announced a conference to tackle corruption and said he would take care to ensure his ministers were "competent and just".
Mr Karzai, who was re-elected in a poll marred by fraud allegations, is expected to name his new cabinet in coming weeks.
Correspondents say they will wait to see the new line-up to get a real idea of how serious Mr Karzai is about tackling corruption.
They will also want to see if any corruption investigations lead to charges resulting in convictions.
Mr Faqiryar told the BBC that some of those people under investigation had already presented themselves for questioning.
Interpol had been asked for help to bring back to Afghanistan others who were abroad, he said.
US ambassador Karl Eikenberry says Afghans must act against corruption
As well as current and former ministers, Mr Faqiryar said two officials from the Ministry of Hajj and Religious Affairs were under investigation.
He said they were suspected of illegally receiving hundreds of thousands of dollars relating to payments for accommodation for Afghan pilgrims attending the Hajj in Saudi Arabia.
Mr Faqiryar said the various investigations should be completed within weeks.
The development comes a week after Afghan officials announced the launch of a new force to fight corruption.
US ambassador Karl Eikenberry, who has warned against a large US troop increase unless Mr Karzai takes action against corruption, said the announcement would need to be followed by concrete action.
"Words are cheap. Deeds are required," he said.
Previous Afghan efforts have done little to curtail corruption.
US President Barack Obama is expected to announce a decision soon on whether to send more American troops to Afghanistan, following weeks of deliberation.
US officials say he wants to be sure that Mr Karzai is a reliable partner.
Last week, US Secretary of State Hillary Clinton Clinton warned that the US would not give civilian aid to Afghanistan unless it could track how it was used.
Earlier this month, Afghanistan's chief prosecutor said he had a list of senior officials, including current and former ministers, who were suspected of receiving illegal payments related to government contracts.