Last month, Faisal bin Ali Jaber traveled from his home in Yemen to Washington to ask why a United States drone had fired missiles at, and killed, his brother-in-law, a cleric who had spoken out against al-Qaida. Also killed in the attack was Jaber's nephew, a policeman who had come to offer protection to his uncle.

Congressional representatives and government officials met Jaber and expressed their condolences, but provided no explanations. Nor has the U.S. admitted that it made a mistake.

A week later, Gen. Joseph F. Dunford Jr., the U.S. and NATO commander in Afghanistan, did apologize for a drone attack that killed a child and seriously wounded two women in Afghanistan's Helmand Province. The incident's timing was particularly unfortunate, as it coincided with efforts to reach an agreement to keep a residual deployment of U.S. troops in Afghanistan beyond the planned 2014 departure of foreign combat forces.