Three U.S. soldiers were shot and wounded on Sunday in what appeared to be an insider attack by a member of the Afghan armed forces. The U.S. military identified the attacker as an Afghan officer, saying he opened fire on the Americans at a base in Helmand province. Coalition security forces returned fire to “end the attack,” and killed the alleged attacker, Navy Capt. Bill Salvin said. The shooting occurred during a military training exercise. Such “green on blue” attacks were common years ago, but became rare after most foreign troops left Afghanistan in 2014.