Government spokesman Konrad Ciesiolkiewicz would not comment on Tuesday on any findings made by the investigation, which Kazimierz Marcinkiewicz, the prime minister, ordered in early December.
"The case was closed last week," Ciesiolkiewicz said.
He said Zbigniew Wassermann, the minister in charge of intelligence services, coordinated the investigation.
Wassermann's report was delivered to a parliamentary commission in a closed-door session last week, and members of the panel declared themselves fully satisfied and decided to drop any further investigation.
The spokesman said the government did not plan a separate announcement of the findings.
Allegations that the CIA may secretly have held terror suspects on Polish territory were raised by the New York-based Human Rights Watch.
Polish officials have denied them vehemently.