The United Nations has called on the United States to reveal civilian casualties caused by its assassination drone strikes.
A UN investigation, conducted by Special Rapporteur Ben Emmerson and reported on Friday, accused the US of defying international legal norms by using lethal force outside war zones.
The investigation found that US drone strikes have killed more than 450 civilians in Afghanistan, Pakistan and Yemen over the past decade.
The report added that the US is obliged to probe reported civilian casualties and explain its legal justifications for the deadly strikes.
Launched in January, the investigation offers a review of the legality of terror drone strikes.
Emmersons investigation reported that 2,200 people, including 400 civilians, have died in the US drone strikes in Pakistan during the past decade.
[Pakistani] Officials indicated that, owing to underreporting and obstacles to effective investigation, those figures were likely to be an underestimate, he wrote.
A similar UN report on Thursday warned that the use of armed drones threatens global security and encourages more states to acquire unmanned weapons.
The report, which has been submitted to UN General Assembly by Christof Heyns -- the organizations special rapporteur on extrajudicial killings, summary or arbitrary executions -- called for states that operate armed drones to be more transparent and publicly disclose how they use them.
Washington uses assassination drones in several countries, claiming that they target terrorists. According to witnesses, however, the attacks have mostly led to massive civilian casualties.