The newspaper reports that prosecutors have opened a criminal probe of Mahmood Karzai, as the U.S. struggles to push counterterrorism efforts while cracking down on corruption within the Karzai government in Afghanistan.
According to the newspaper, prosecutors are weighing charges of tax evasion, racketeering or extortion against Mahmood Karzai, who is a U.S. citizen.
Karzai denied any wrongdoing, telling the newspaper that he built his wealth legitimately.
"They won't find anything. I'm just a businessman," he said.
This isn't the first time Karzai's brother has been linked to questionable business dealings. Earlier this month, two top executives of Kabul Bank resigned amid. The bank's third-largest shareholder: Mahmood Karzai.
The bank's woes tie into the web of corruption and personal connections that has soured many Afghans on their government.