The White House is refusing to comment on reports U.S. spy networks have been uncovered in Iran and Lebanon, in what would be a significant setback for U.S. intelligence efforts.

White House spokesman Jay Carney told reporters Monday he would not comment on intelligence matters. But separately, U.S. officials have confirmed to reporters that Iran and Lebanon-based Hezbollah have identified a number of spies. Officials say many have already been, or are in danger of being, executed.

The agents were paid informants working for the Central Intelligence Agency, and they were helping the U.S. gather information about Iran's nuclear programs and the activities of Hezbollah, considered by the U.S. a terrorist organization.

Some officials said being discovered is one of the dangers of being a spy. But some officials familiar with the situation say there are also indications the CIA may have failed to take adequate precautions to keep its informants safe.