U.S. officials say Pakistan has apparently tipped off militants at two more bomb-building factories in its tribal areas, giving the terror suspects time to flee.
U.S. intelligence had shared the locations with the Pakistani government.
One official says this was intended to give Pakistan another chance to build trust after the U.S. raid on May 2 that killed Osama bin Laden in Abbottabad.
The latest incident brings to a total of four bomb-making sites the U.S. has shared with Pakistan, only to have the terrorist suspects flee before the Pakistani military arrived much later.
The U.S. officials believe Pakistan's insistence on seeking local tribal elders' permission before raiding the areas may have most directly contributed to the militants' flight, though they also suspect low-level security officials may have tipped the militants off.
All officials spoke on condition of anonymity to discuss matters of intelligence.