The report quoted American and Pakistani officials as saying that al-Qaeda and several Pakistani militant factions have been emboldened by the lull in drone strikes, which have helped them "regroup, increase attacks against Pakistani security forces and threaten intensified strikes against allied forces in Afghanistan."
After tensions between the US and Pakistan plunged to new low following the NATO attack, the CIA has not conducted a drone strike since mid-November as it hopes to avoid making matters worse while Islamabad completes a wide-ranging review of its security relationship with Washington, the report said.
It said pause in CIA missile strikes, which has been the longest in Pakistan in more than three years, is for the time being offering "greater freedom of movement to an insurgency that had been splintered by in-fighting and battered by American drone attacks in recent months."
Feuding factions in militant groups have said that they were patching up their differences to focus on fighting Americans in Afghanistan, while other militant groups continue to attack Pakistani forces.
Drone strikes in Pakistan dropped to 64 last year as against 117 strikes in 2010, according to The Long War Journal, a website that monitors the attacks.