JUBA (Reuters) - Gunmen in famine-hit South Sudan killed two people and wounded three when they attacked a humanitarian convoy in the center of the country, the International Organization for Migration (IOM) said in a statement on Thursday.

South Sudan, the world’s youngest nation, has been mired in conflict since President Salva Kiir, an ethnic Dinka, fired his deputy Reik Machar, a Nuer, in 2013. The subsequent civil war split the nation along ethnic lines and has forced more than 3 million people to flee their homes.

Nearly half the population, or about 5.5 million people, is expected to lack a reliable source of food by July, and last month the United Nations said parts of the country are already suffering from famine.

Aid workers have been kidnapped, shot at and had their supplies looted by armed men.

“While a convoy was returning to Yirol from a field mission on 14 March, one of the vehicles was ambushed by unknown armed gunmen. Tragically, two people died of gunshot wounds. Among the injured was an IOM health officer who sustained a gunshot wound but is currently in a stable condition,” the IOM statement said.

Yirol, where the aid workers had been treating a cholera outbreak, is about 210 km (130 miles) northwest of the capital of Juba.

The identity and motivation of the attackers are unknown, the statement said.

Also on Thursday, medical aid group Médecins Sans Frontières/Doctors Without Borders (MSF) said its hospital in Wau Shilluk had been looted during recent heavy fighting.

“Wau Shilluk was looted of all medicines including life-saving drugs and essential supplies,” Abdalla Hussein Abdalla, the deputy head of mission for South Sudan, said in a statement. “Our hospital is in a terrible condition.”

Earlier this week, gunmen briefly detained eight local employees of U.S. charity Samaritan’s Purse.