The Afghan president has admitted his office received secret payments from the US, but says the amounts were small and used legitimately.
Hamid Karzai was responding to a New York Times report that alleged the CIA sent suitcases stuffed with cash to the president's office on a regular basis.
It said tens of millions of dollars "came in secret" and cash was given on a vaster scale than previously thought.
The president said the money was for projects such as helping the sick.
"It was used for different purposes: operational, assistance to injured people, rental costs and other goals. This was efficient assistance and we appreciate it," he said in a statement.
He added that the money had been delivered to Afghanistan's National Security Council, which is part of the president's office, during the last 10 years.
The New York Times report said: "Wads of American dollars packed into suitcases, backpacks and, on occasion, plastic shopping bags have been dropped off every month or so at the offices of Afghanistan's president."
It quoted Khalil Roman, who was Mr Karzai's chief of staff from 2002 until 2005, as saying the cash was referred to as "ghost money".
"It came in secret, and it left in secret," Mr Roman is quoted as saying.
The report cited unnamed US officials' assessments that there was little evidence the payment bought the influence the CIA sought, and said that the cash was not subject to the conditions placed on official US aid.
It added that much of the money fuelled corruption and went to paying off warlords and politicians with dubious connections.
The CIA declined to comment on the New York Times report, as did the US state department.
In 2010, Mr Karzai acknowledged that his office has received cash from Iran, but insists this was part of a "transparent" process. He said the money was not for an individual, but to help run the president's office.
Afghanistan receives billions of dollars in aid, but remains one of the poorest countries in the world.