Ben Emmerson, the lawyer leading a UN drone inquiry, has praised President Barack Obama's speech as a significant step towards increased transparency.
Emmerson said Obama had set out more clearly than ever before the legal justifications for targeted killing.
According to the BBC, Emmerson, a United Nations human rights special rapporteur, launched an inquiry into drones in January, saying their use represents a real challenge to the framework of international law.
In a statement, he said Obama's speech had broken new ground on a number of issues, adding that it sets out more clearly and more authoritatively than ever before the administration's legal justifications for targeted killing, and the constraints that it operates under.
In his speech, Obama pledged to continue strikes, but with tighter oversight of the programme and stricter targeting rules.