A United Nations investigation has found that American drone strikes have killed at least 400 civilians in Pakistan, far more than the US has ever acknowledged.
Ben Emmerson, UN special rapporteur, accused the US of challenging international legal norms by advocating the use of lethal force outside war zones.
The investigation was launched in January and had been due to be completed by the autumn, offering a review of the legality of drone strikes and an analysis of the number of civilian casualties – totalling almost 500 across the world.
However, Mr Emmerson said gathering direct data on individual drone strikes – which generally occur in remote, hostile locations – had taken longer than expected and his report would not be complete until next year.
Instead, he has issued an interim report which is due to be debated at the UN next week.