His comments come after warnings from the UN and others that Afghanistan could see billions in international asistance dry up unless his new government tackles corruption.
But he dismissed allegations widely made against top officials, including his brother, Wali -- widely accused of being involved in the opium trade.
Karzai said he had asked US and European officials to present evidence of his brothers alleged corruption, but there was "never an answer."
"Where we have found such corruption, we have addressed it," he said, adding that allegations his brother also worked for the CIA "doesn't surprise me at all," because the CIA was "in contact with a lot of people."
Karzai, long supported by western governments, has seen ties with the west sour dramatically since he was re-elected in a widely condemned poll earlier this year.
The poll coincided with a sharp upturn in violence and as US president Barack Obama weighted the possibility of sending tens-of-thousands more troops to the country to quell the bloodshed and tackle insurgents.
The UN recently announced it would withdraw more than 50 percent of its international staff, or 600 people, in the wake of an attack on a Kabul guesthouse that killed five UN staff.
Karzai said the move would have "no impact."
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