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U.S. citizen Warren Weinstein and Italian national Giovanni Lo Porto were hostages of al Qaeda — unlike the terrorists usually in the crosshairs of armed U.S. drones — and their inadvertent deaths have revived the debate over whether such killings are good policy.

President Obama and congressional leaders promised to investigate how the two kidnapped aid workers died. But what's already known about the attack, which occurred in January but was only disclosed on Thursday, was enough to raise new questions about the administration's heavy reliance on drone strikes to fight Islamist terrorists.

The White House also disclosed Thursday that two other U.S. citizens who also were wanted al Qaeda terrorists were killed in January. Ahmed Farouq was killed in the same strike that killed Weinstein and Lo Porto; Adam Gadahn, the first American indicted for treason since World War II, died in a separate strike.

Those deaths bring to seven the total number of U.S. citizens killed in drone strikes aimed at suspected terrorists since Sept. 30, 2011, when al Qaeda leader Anwar al-Awlaki was killed in Yemen. In addition to Yemen, U.S. drones have targeted suspected terrorists in Pakistan, Afghanistan, Somalia and Syria.

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