The Obama administration plans to arm Italy’s fleet of Reaper drone aircraft, a move that could open the door for sales of advanced hunter-killer drone technology to other allies, according to lawmakers and others familiar with the matter. The sale would make Italy the first foreign country besides Britain to fly U.S. drones armed with missiles and laser-guided bombs. U.S. officials said Italy intends initially to deploy the armed drones in Afghanistan. Lawmakers who question the planned deal say the decision to “weaponize” Italy’s unarmed surveillance drones could make it harder for the U.S. to deny similar capabilities to other...