The United Nations says it is “alarmed” by Monday's air raids on a South Sudan refugee camp holding about 5,000 people who had fled violence in neighboring Sudan.

A statement from the U.N. refugee agency Tuesday said the raid took place in the Upper Nile state town of Elfoj, about 10 kilometers from the Sudanese border. A child was wounded in the raid and 14 other refugees are missing.

The agency did not say who carried out the strikes. South Sudan has accused Sudan of bombing its territory in the past.

U.N. officials say the bombings targeted refugees who were especially vulnerable because they had just fled violence in Sudan's Blue Nile state.

The United Nations says that since August more than 78,000 people have fled fighting in Sudan's Blue Nile and Southern Kordofan states along the border. Sudan has been battling rebels it says are aligned with South Sudan, which declared independence in July.

Aid groups say fighting along the border area has moved closer to refugee camps in South Sudan, and that humanitarian workers are working to transfer the refugees farther south.

The U.N. says a massive humanitarian effort is needed to handle the flow of refugees into South Sudan.

The world body also has expressed concern about the humanitarian needs of people who remain in Sudan's Blue Nile and Southern Kordofan states. Sudan has denied requests by humanitarian groups to assess the needs of people in the troubled states and provide them with aid.

Also Tuesday, Russia said it is ending its participation in the U.N. peacekeeping mission in South Sudan. President Dmitry Medvedev said Russian peacekeepers made a meaningful contribution to South Sudan's transformation into an independent state.

Russia plans to have all its troops and helicopters out of South Sudan by April.