South Sudan's army admitted it shot down a United Nations peacekeeping helicopter in the restive Jonglei state on Friday, killing the four Russian crew members onboard. South Sudan's army first denied it had shot down the Russian helicopter but later said it had mistaken it for a Sudanese plane supplying Yau Yau rebels in Jonglei. U.N. Secretary-General Ban Ki-moon strongly condemned the attack on the "clearly marked" helicopter and in a statement called "on the government of South Sudan to immediately carry out an investigation and bring to account those responsible for this act."