Russia on Saturday urged South Sudan to punish those responsible for shooting down a UN helicopter, killing all four Russian crew members on board.

"We call on the government of South Sudan to carry out the necessary investigation, punish the guilty and take every measure to guarantee that this never happens again," the foreign ministry said in a statement on its website after Friday's incident.

It named the men who died as S. Ilyin, the pilot, A. Abrarov, the second pilot, S. Yegorov, the flight engineer, and N. Shpanov, the cabin attendant and radio operator.

UN leader Ban Ki-moon reacted furiously to the attack by the South Sudan army which brought down the peacekeepers' helicopter over the eastern Jonglei state.

He said it was a "clearly marked" UN aircraft and demanded that those responsible be brought to account. The UN Security Council and US government both deplored South Sudan's action.

A South Sudan military spokesman said troops fired anti-aircraft guns at the Russian MI-8 believing it was a rebel helicopter carrying weapons to anti-government forces.