Senate Majority Leader Bill Frist says he is more concerned about the leak of information regarding secret CIA detention centers than activity in the prisons themselves.

Frist told reporters Thursday that while he believed illegal activity should not take place at detention centers, he believes the leak itself poses a greater threat to national security and is "not concerned about what goes on" behind the prison walls.

"My concern is with leaks of information that jeopardize your safety and security — period," Frist said. "That is a legitimate concern."

He noted that the number of sensitive national security issues, including the existence of secret CIA detention centers for suspected terrorists in Eastern European democracies. The Bush administration has neither confirmed nor denied that report.

Frist was asked if that meant he was not concerned about investigating what goes on in detention centers.

"I am not concerned about what goes on and I'm not going to comment about the nature of that," Frist replied.

He added that as Senate majority leader he is privy to classified information and discussions about prison activity. "I'm going to make sure that everything that's done is consistent with the Constitution ... and the laws of the United States of America," he said.

Frist and House Speaker Dennis Hastert, R-Ill., wrote the leaders of the House and Senate intelligence committees earlier this week calling for a joint congressional investigation into the leak.

"What is the actual and potential damage done to the national security of the United States and our partners in the global war on terror?" the letter said, referring to the leak.

The Post's story said the CIA has been hiding and interrogating some of its most important al-Qaida captives at a Soviet-era compound in Eastern Europe, part of a covert prison system set up by the agency four years ago that at various times has included sites in eight countries. Those countries, the Post said, include several democracies.