MOSCOW (Reuters) - Russia called on South Sudan on Saturday to punish those responsible for shooting down a U.N. helicopter, killing its four Russian crew, and take steps to ensure such incidents do not happen again.

A Russian Foreign Ministry statement named the victims and said the "tragic occurrence" in the African nation on Friday underscored the need to provide security for U.N. peacekeeping missions.

"We call on the government of South Sudan to conduct a proper investigation of the incident, to punish those responsible and undertake all measures to guarantee nothing like this happens in the future," it said.

The Mi-8 helicopter owned by Russian air charter company Nizhnevartovskavia was working under a U.N. contract on a reconnaissance mission in an area where the SPLA, South Sudan's army, has been fighting rebels led by David Yau Yau, according to a U.N. source.

The SPLA first denied it had shot down the helicopter but later said it had mistaken it for a Sudanese plane supplying rebels, and expressed regret.

The Russian statement said that the downing "raises the issue of the provision of security of U.N. peacekeeping missions with new acuteness", and that host nations must take the issue extremely seriously.

(Writing by Steve Gutterman; Editing by Nastassia Astrasheuskaya and Richard Meares)