Russia has urged the South Sudanese authorities to conduct a full investigation into the UN helicopter accident in which four Russians were killed, RIA Novosti reported.

A Mil Mi-8 helicopter was shot down Friday, December 21 on a reconnaissance flight in South Sudan’s eastern state of Jonglei, the UN said in a statement. All four Russian crew members on board were killed. South Sudan’s army apologized for the downing as soldiers mistook the helicopter for an aircraft carrying arms to rebel forces, Philip Aguer, a spokesman for the military, said earlier on Saturday.

“We are calling on the South Sudanese government to conduct a full-scale investigation into the accident, punish those guilty and implement all measures to guarantee such things do not happen again,” the Russian Foreign Ministry said in a statement posted on its website Saturday.