UN investigator presses US to publish drone attack data
A United Nations investigator has called on the US to make public its data about drone strikes and civilian casualties.
Ben Emmerson has spent the year travelling to countries where the strikes have taken place, and speaking to US officials.
He says the involvement of the CIA creates "an almost insurmountable obstacle to transparency".
In Pakistan he was told at least 400 civilians had been killed since 2004.
The Obama administration's policy of using drones in places such as Pakistan, Afghanistan and Yemen - chiefly to carry out deadly missile attacks against suspected militants - has come under increasing criticism.
Mr Emmerson, a British lawyer who acts as the UN special rapporteur on human rights and counter-terrorism, has prepared an interim report for the UN's Human Rights Council on his work since January 2013.
There have been estimates by independent groups of the number of civilian deaths caused by drone strikes but no real hard data from the US. It is not even clear how the US classifies who is a civilian and who is not.
This leads on to important legal questions about when strikes might be justified - what constitutes self-defence? How imminent does a threat need to be? What about consent from the state where an attack takes place?
The message from the UN special rapporteur is that there will need to be more transparency about the impact of strikes as well as agreement about the laws under which they operate.
In the report he writes that he cannot accept that national security considerations justify the US withholding its own data on civilian casualties from the pilotless operations.
He also says there a number of legal questions relating to the use of drones which urgently need to be resolved internationally.
However he does conclude that, if used in compliance with humanitarian law, remotely piloted aircraft are capable of reducing the risk of civilian casualties in armed conflict.
The BBC's security correspondent, Gordon Corera, says the fear highlighted in Mr Emmerson's report is that without any consensus on how drones could be used, their use will become increasingly widespread and dangerous.
Drones may be controversial, but the signs are that they are here to stay and many more countries may begin to use them, our correspondent adds.