The Guardian reports: The US policy of using aerial drones to carry out targeted killings presents a major challenge to the system of international law that has endured since the second world war, a United Nations investigator has said.

Christof Heyns, the UN special rapporteur on extrajudicial killings, summary or arbitrary executions, told a conference in Geneva that President Obama’s attacks in Pakistan, Yemen and elsewhere, carried out by the CIA, would encourage other states to flout long-established human rights standards.

In his strongest critique so far of drone strikes, Heyns suggested some may even constitute “war crimes”. His comments come amid rising international unease over the surge in killings by remotely piloted unmanned aerial vehicles (UAVs).

Addressing the conference, which was organised by the American Civil Liberties Union (ACLU), a second UN rapporteur, Ben Emmerson QC, who monitors counter-terrorism, announced he would be prioritising inquiries into drone strikes.

The London-based barrister said the issue was moving rapidly up the international agenda after China and Russia this week jointly issued a statement at the UN Human Rights Council, backed by other countries, condemning drone attacks.

If the US or any other states responsible for attacks outside recognised war zones did not establish independent investigations into each killing, Emmerson emphasised, then “the UN itself should consider establishing an investigatory body”.