Deploying drone strikes as a form of global policing undermines international security and will encourage more states and terrorist groups to acquire unmanned weapons, a UN report has warned.
The study has been submitted to UN general assembly by Christof Heyns, a South African law professor who is the organisation's special rapporteur on extra-judicial, summary or arbitrary executions.
Although no state is identified in the report, the comments are clearly directed at the legal problems raised by the US programme of aerial attacks against al-Qaida supporters in Pakistan, Yemenand elsewhere.
"The expansive use of armed drones by the first states to acquire them, if not challenged, can do structural damage to the cornerstones of international security and set precedents that undermine the protection of life across the globe in the longer term," the report states.
"The use of drones by states to exercise essentially a global policing function to counter potential threats presents a danger to the protection of life, because the tools of domestic policing (such as capture) are not available, and the more permissive targeting framework of the laws of war is often used instead."
Heyns's report is due to be debated at the UN general assembly in New York on 25 October. It calls for international laws to be respected rather than ignored. The US has said that its use of drones against al-Qaida is an act of self-defence and permissible as part of the administration's global "war on terror".
The rapporteur notes: "Drones come from the sky but leave the heavy footprint of war on the communities they target.
"The claims that drones are more precise in targeting cannot be accepted uncritically, not least because terms such as 'terrorist' or 'militant' are sometimes used to describe people who are in truth protected civilians.
"Armed drones may fall into the hands of non-state actors and may also be hacked by enemies or other entities. In sum, the number of states with the capacity to use drones is likely to increase significantly in the near future, underscoring the need for greater consensus on the terms of their use."
Intentional killing is only permitted when protecting against an imminent threat to life, the report comments. "The view that mere past involvement in planning attacks is sufficient to render an individual targetable, even where there is no evidence of a specific and immediate attack, distorts the requirements established in international human rights law."
Countries cannot consent "to the violation of their obligations under international humanitarian law or international human rights law", Heyns says, in a passage that may be aimed at countries such as Pakistan and Yemen where US drone strikes regularly occur.
The report was welcomed by the London-based human rights group Reprieve, which represents several civilian victims of drone strikes in Pakistan and Yemen.
Its legal director, Kat Craig, said: "This report rightly states that the US's secretive drone war is a danger not only to innocent civilians on the ground but also to international security as a whole.
"The CIA's campaign must be brought out of the shadows: we need to see real accountability for the hundreds of civilians who have been killed – and justice for their relatives. Among Reprieve's clients are young Pakistani children who saw their grandmother killed in front of them – the CIA must not be allowed to continue to smear these people as 'terrorists.'"