A prominent U.S. newspaper reports U.S. intelligence officials have twice provided information to Pakistan about the specific locations of insurgent bomb-making factories, only to find the sites abandoned before Pakistani troops arrived.

The Washington Post reported Friday that U.S. officials say they do not know how the operation was compromised.

The newspaper says the U.S. handed over surveillance video and other information about the bomb-making sites in mid-May to Pakistan as part of a “trust-building effort,” following the killing of al-Qaida leader Osama bin Laden in a U.S. raid on Pakistan soil early last month.

The publication reports U.S. officials are ''concerned” the information was leaked inside Pakistan, or the insurgents were warned directly by Pakistan's spy agency.

The Washington Post says a senior Pakistani military official said Friday the U.S. had also shared information about weapons storage facilities that were also found empty.

Pakistan has consistently denied that its security services are providing information to militants.

Ties between Pakistan and the U.S. have been strained since the discovery of bin Laden living in Pakistan, not far from a military academy.