A foreign-funded inquiry on Wednesday reported on how a $900 million fraud ruined the Kabul Bank, how cash was smuggled abroad in airline food trays, and said top politicians dictated who should be prosecuted over the theft.

The inquiry did not name Karzai, but hinted that the president himself benefited, saying the bank had "reportedly provided millions of dollars to the campaign of at least one presidential candidate" against central bank advice.

Kabul Bank was reported to have been a major donor to Karzai's 2009 re-election campaign, which was itself tainted by fraud and voting irregularities.

"The president is not aware (of the payments to his campaign)," presidential spokesman Aimal Faizi told AFP.

"He learnt of claims that $20 million was paid to his campaign. This is a lot of money. We will investigate this."

The president had specifically told the chairman and CEO of the bank in a meeting at his office that if they were asked to contribute to his campaign they should refuse, Faizi said.

The 87-page findings of the inquiry expose a sophisticated network of corruption that saw money smuggled abroad, as well as political interference in criminal proceedings.

Critics, including international corruption watchdog Global Witness, point out that the report also reveals an urgent need for international banking reform.