Citing a "dramatic increase" in the United States' use of targeted killings in the last few years, the UN Special Rapporteur on Extrajudicial Killings has just released a report (PDF) decrying the lack of accountability in the U.S. overseas killings by unmanned drones.

"Disclosure of these killings is critical to ensure accountability, justice and reparation for victims or their families," UN investigator Christof Heyns said in his followup to a 2010 UN report criticizing U.S. practices.

The (U.S.) government should clarify the procedures in place to ensure that any targeted killing complies with international humanitarian law and human rights and indicate the measures or strategies applied to prevent casualties, as well as the measures in place to provide prompt, thorough, effective and independent public investigation of alleged violations.

Citing Pakistani Human Rights Commission figures, Heyns said thousands have been killed in 300 drone strikes in Pakistan alone since 2004. About 20 percent of the dead are believed to be civilians, according to the Pakistani commission, the Bureau of Investigative Journalism, and the New America Foundation. Although U.S. officials dispute those figures, a new ProPublica report finds that the United States' own estimates of civilian casualties contradict one another.

Human rights law requires that nations make every effort to arrest a suspect, in line with the "principles of necessity and proportionality on the use of force," Heyns said in his report, adding that the United States had failed to respond to the concerns of his predecessor, Philip Alston.