DUBAI, UNITED ARAB EMIRATES - Struggling to contain an escalating crisis at Kabul Bank, Afghan authorities have barred the sale of Kabul properties held by the bank's principal owners.

But the freeze excludes President Hamid Karzai's brother, Kabul Bank's third largest shareholder, who says he does not own property in the Afghan capital.

The Afghan Central Bank ordered the property-sale ban in a letter reviewed by The Washington Post. It was sent to Kabul municipal authorities and it targets five people, including Kabul Bank's two biggest shareholders - who were ousted last Monday as executives of the bank - as well as the brother of Afghanistan's vice president, who is both a shareholder and major borrower.

No restrictions were placed on the president's own brother, Mahmoud Karzai, who has also borrowed money from Kabul Bank, including $6 million that he used to buy a 7 percent stake in the crumbling bank.

"They couldn't freeze my property because I don't have it," Mahmoud Karzai said in a telephone interview from Kabul. "I don't have a single house or parcel of land in my name in Afghanistan."

Afghans frequently register their assets in the names of relatives or trusted friends. Critics of the Karzai family allege that Mahmoud has done this, but others dismiss such claims as a politically motivated smear.

Mahmoud Karzai holds a stake in an Afghan cement factory and is involved in a Kandahar property development, but when in Kabul, he stays in a rented property. He spends much of his time in Dubai, where he lives in a luxury villa purchased for $5.5 million with Kabul Bank funds. His principal asset, he said, is a house in Maryland, which he rents out.

The move to block asset sales comes as Afghan authorities struggle to hold the nation's largest bank together against waves of depositors demanding their money back. Amid reports that bank funds have been stolen in several cities, authorities want to try to stop bank insiders from selling assets purchased with loans that haven't been repaid.

The disarray at Kabul Bank, which still has more than 1 million customers and handles salary payments for soldiers, police and teachers, flows from a tangle of murky loans by shareholders to themselves and from risky investments in Dubai real estate. With so many Afghans' savings, salaries and political fortunes at stake, what began as a financial mess has morphed into a serious challenge to the credibility of President Karzai and his American backers.

Washington has ruled out using any American money for a bailout, despite fears that the collapse of Kabul Bank could leave soldiers unpaid and set back the fight against the Taliban, a struggle in which the United States has already lost more than 1,100 troops and has spent billions of dollars. During their own years in power in Kabul from 1996 to 2001, the Taliban banned private banks.

The central bank letter was signed by Noor Ahmad, head of the general office. It was first obtained by Tolo News, an Afghan 24-hour news channel. Central bank officials could not be reached for comment.

Some Afghan officials want the central bank to seize shares in Kabul Bank that were not paid for in cash. Around half the shares - including those of the president's brother and also of the brother of the vice president - were purchased with Kabul Bank loans. These loans, said Kabul Bank's founder and former chairman Sherkhan Farnood, are all still outstanding. Transferring the shares would lead in effect to the partial nationalization of Kabul Bank.