Classified intelligence reports reveal that the CIA did not always know who it was targeting and killing in terror drone strikes in Pakistan over a 14 - month period.

According to NBC News, the classified reports show that about one of every four of those killed by drones in Pakistan between Sept. 3,2010, and Oct. 30,2011, were classified as " other militants. "

The " other militants " label was used when the CIA could not determine the affiliation of those killed, prompting questions about how the agency could conclude they were a threat to US national security.

The report added the uncertainty appears to arise from the use of so - called " signature " strikes to eliminate suspected militants - picking targets based in part on their behavior and associates. A former White House official said the US sometimes executes people based on " circumstantial evidence. "

Three former senior Obama administration officials also told NBC News that some White House officials were worried that the CIA had painted too rosy a picture of its success and likely ignored or missed mistakes when tallying death totals.

NBC News has reviewed two sets of classified documents that describe 114 drone strikes over 14 months in Pakistan and Afghanistan, starting in September 2010. The documents list locations, death and injury tolls, alleged militant affiliations, and whether the killed and injured were deemed combatants or non - combatants.

Though the Obama administration has previously said it targets al - Qaeda leaders and senior Taliban officials plotting attacks against the US and American troops, " officials are sometimes unsure of the targets ' affiliations, " NBC News reported, adding that about half of the targets in the documents are described as al - Qaeda. But in 26 of the attacks, accounting for about a quarter of the fatalities, those killed are described only as " other militants. " In four others, the dead are described as “foreign fighters. ”

In some cases, US officials also seem unsure how many people died. One entry says that a drone attack killed seven to 10 people, while another says that an attack killed 20 to 22, said the report.

However, NBC News said, officials seem certain that however many people died, and whoever they were, none of them were non - combatants. In fact, of the approximately 600 people listed as killed in the documents, only one is described as a civilian. The individual was identified to NBC News as the wife of an al - Qaeda leader.

Micah Zenko, a former State Department policy advisor who is now a drone expert at the Council on Foreign Relations, was quoted by NBC News as saying it was " incredible " to state that only one non - combatant was killed.

" It’s just not believable, " he said. " Anyone who knows anything about how airpower is used and deployed, civilians die, and individuals who are engaged in the operations know this. "

President Barack Obama recently narrowed the scope of the US targeted - killing campaign against al - Qaeda and its allies and claimed the US would only use drone strikes when a threat was " continuing and imminent, " a nuanced change from the previous policy of launching strikes against a significant threat.

The United States uses its killer drones in a number of countries including Afghanistan, Pakistan, Yemen and Somalia, claiming the targets of the attacks are militants, but local officials and witnesses say civilians have been the main victims.

According to data released by the Pentagon in February, Afghanistan is becoming a “drone war” with a 72 - percent increase in the number of drone strikes from 2011 to 2012. The United States carried out over 500 drone attacks in Afghanistan last year, the Pentagon said.