Jeh Johnson is the top lawyer at the Pentagon and says America's counter terrorism measures can be justified under US and international law.
The US has increased the number of drone strikes since President Obama first took office.
Mr Johnson told HARDtalk's Zeinab Badawi that the new technology enabled high value terrorists to be targeted with great precision but the US Military did its best to minimise civilian casualties as the loss of innocent lives was never acceptable.
You can watch the full interview on BBC World News on Thursday 28 November at 04:30, 09:30, 15:30 and 21:30 GMT and on the BBC News Channel on Friday 30 November at 00:30 GMT and 04:30 GMT.
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