Seven American service members, including a senior U.S. officer, were killed this week in Afghanistan in three separate attacks. Three U.S. Marines were killed and a fourth Marine seriously wounded late Thursday in southern Afghanistan by a man wearing an Afghan army uniform, NBC News reported. According to Reuters, an Afghan police commander opened fire on the group after having invited them to a meeting in Sarwan Qala, Helmand Province to talk security. The shooter escaped into darkness, NBC News reported. In a separate attack in northeastern Kunar province Wednesday, the Pentagon confirmed that a suicide bomber killed a senior U.S. officer, two majors and an American aid worker. The dead included Command Sgt. Maj. Kevin J. Griffin, the most senior enlisted soldier for the 4th Brigade Combat Team, 4th Infantry Division, and a Bronze Star recipient, NBC News reported. Maj. Thomas E. Kennedy, 35, of West Point, N.Y., and Air Force Maj. Walter D. Gray, 38, of Conyers, Ga., were also killed, along with USAID foreign service officer Ragaei Abdelfattah. On Tuesday, two gunman wearing Afghan uniforms killed a U.S. soldier in eastern Paktia province. There have been 24 attacks on foreign troops since January, which claimed the lives of 28 people, according to NATO.