Former President Bill Clinton says he had “serious reservations” about covertly listening to phone conversations or reading emails of other world leaders during his time in the Oval Office.

“Well, it depended on who they were,” Clinton told Jorge Ramos on Tuesday. “If we thought they were engaged in hostile acts against the United States…then [American agencies] might do it. But — I’m not sure — we didn’t have the capability then to do a lot of what’s being done today.”

Since June, several media outlets have published leaked information about the broad spying powers wielded by the National Security Agency (NSA) under the aegis of President Obama. The agency has collected nearly all U.S. call records and captured millions of email contact lists.

The NSA also spied on at least 35 world leaders, including allies in Mexico, Brazil and Germany. That has led to rebukes from officials like Mexico’s ambassador to the U.S., who said the data collection was “unacceptable.”

Clinton said on Tuesday that the spying scandal has hurt U.S. relations around the globe.

“I do think that the stories about the data collection has had a damaging effect,” he said. “And not just in Latin America, but in Europe and Asia. Now, it’s interesting because in some other countries it’s come out that those governments were doing the same thing, or that other governments had given us permission.”

Speaking with Ramos at his home in Chappaqua, New York, Clinton called for a more robust public debate on how to balance privacy and security concerns.

“What we need here is more transparency and more privacy and more security,” he said. “We’re getting in a position here where people didn’t know what was going on. And the way the data’s been handled, it’s not clear that it’s maximized our security, and it’s perfectly clear that it’s eroded some people’s sense of privacy. So I think the most important thing we can do now is have a really public discussion about what the rules should be.”

Clinton also called for more clarity between nations in how they proceed with intelligence gathering.

“I think there ought to be very explicit rules on listening in on conversations of world leaders,” he said.

On December 8, Clinton will convene regional and global leaders in Rio de Janeiro to discuss policy issues as part of the Clinton Global Initiative, a project he started in 2005.