Officials say the sites were empty when Pakistani soldiers reached them in early June, The Washington Post reported Saturday. A senior official told the Post there had been similar recent incidents, including at places used to store weapons.
"There is a suspicion that perhaps there was a tip-off," he said. "It's being looked into by our people, and certainly anybody involved will be taken to task."
U.S. intelligence on the two bomb factories was provided as part of an effort to rebuild trust with Pakistan after the May 2 raid on Osama bin Laden's compound. U.S. officials told the Post they were unsure if the leak was accidental or if members of Inter-Services Intelligence, the Pakistani intelligence agency, passed the information on to insurgents.
The factories, one in North Waziristan and the other in South Waziristan, were being used to make improvised explosive devices, commonly used against U.S. soldiers in Afghanistan, officials said.