A coterie of well-connected Afghan businessmen and politicians may have plundered as much as $900m from the country's biggest commercial bank, three times the amount of earlier estimates, and the equivalent of about 7 per cent of Afghanistan's total gross domestic product.

Kabul Bank's funds were treated like personal accounts, it is claimed by several well-known members of Afghan society. Mahmoud Karzai, a brother of the Afghan President and prominent shareholder in Kabul Bank, told The New York Times that the bank's former chairman lent himself about $98m (£62m) to buy one of Afghanistan's airlines, and then used deposits to subsidise the carrier in an attempt to drive rivals out of business.

Yet so difficult has the hunt for the missing millions become that the very same man, Sherkhan Farnood, had been brought in to help trace the missing cash. Officials say the value of questionable outstanding loans written by the bank is far greater than originally thought – and auditors poring over the lender's books think up to $800m is potentially unrecoverable.

The crisis is so severe – with fears that a run on the embattled Kabul Bank could lead to its collapse – that Afghanistan's central bank chief, Abdul Qadir Fitrat, was forced yesterday to deny reports that the embattled lender was close to failure. He claimed the sums at stake were smaller than reported and that auditors had been able to account for all but $100m lent to members of Afghanistan's elite.

The case is acutely embarrassing both for President Hamid Karzai, whose tenure has seen Afghanistan turn into a mafia state, and the Obama administration, which has adopted a policy of ignoring institutionalised corruption after several bitter diplomatic spats with Mr Karzai got it nowhere.

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