Of the approximately 2,200 Pakistanis who have died in drone strikes, the report says 400 (18 percent) were not militants, Khaama Press reported Friday.
Ben Emmerson, a U.N. special rapporteur who wrote the report, said that Pakistani officials who provided the number indicate that, "owing to underreporting and obstacles to effective investigation, those figures were likely to be an underestimate."
Some 31 civilians have been killed in drone attacks in Afghanistan and between 12 and 18 in Yemen in the past 18 months, the report added.
The 22-page report was released ahead of a debate on the use of remotely piloted aircraft scheduled for next Friday at the U.N. General Assembly, The Guardian reported.
A related report released Thursday warned drones were being misused as a form of "global policing."
Emmerson contrasted British and U.S. policies on drone usage. He said Britain's Royal Air Force "thoroughly scrubbed" its intelligence before authorizing the use of drones. As a result, he said, there had been only one incident in which civilians were killed.
The CIA's use of drones had created "an almost insurmountable obstacle to transparency," Emmerson said. Consequently, the United States has not revealed any data about the number of civilians killed or injured by drone strikes.
He called on the United States to "further clarify" its policies about the use of drones and to declassify information about the use of drones in counter-terrorism activities.
Emmerson said there was an urgent need to resolve legal issues surrounding the use of drones, the BBC reported.
He added that if drones are used in accordance with international law, the unmanned flying craft could reduce the risk of civilian casualties.