'When news flashed of an airstrike on two cars in the city of Radaa on Sunday afternoon, early claims that 'al Qaeda militants’ had died soon gave way to a more grisly reality. At least 11 civilians had been killed, among them women and three children. It was the worst loss of civilian life in Yemen’s brutal internal war since May 2012. Somebody had messed up badly. But who was responsible – the United States or Yemen?

Local officials and eyewitnesses were clear enough. The Radaa attack was the work of a US drone, a common enough event since the start of the Arab Spring. From May 2011, the Bureau of Investigative Journalism has recorded up to 116 US drone strikes in Yemen, part of a broader covert war aimed at crushing Islamist militants. But of those attacks, only 39 have been confirmed by officials as the work of the United States.'

Read more: Holding the US to Account for Civilian Drone Deaths in Yemen