U.S. President Barack Obama delivers opening remarks during the first plenary session of the Nuclear Security Summit in Washington April 1, 2016. REUTERS/Jonathan Ernst

WASHINGTON (Reuters) - U.S. President Barack Obama said on Friday there is no doubt that civilians have been killed in U.S. drone strikes targeting suspected terrorists, and procedures are constantly evaluated.

He told a news conference at the end of a nuclear security summit that there had been “legitimate criticism” of the legal framework for the drone strikes and “there is no doubt that civilians were killed that shouldn’t have been.”