The ambush on government-controlled territory was the deadliest attack on aid workers since South Sudan's civil war began in 2013. The conflict has killed tens of thousands of people and displaced over three million.
The UN has condemned the killing of six aid workers in South Sudan who were ambushed on government-controlled territory on Saturday. It's the deadliest attack on humanitarian workers since the civil war began in 2013.
The six men from South Sudan and Kenya were ambushed and killed in their vehicle while driving from the capital Juba to Pibor in the country's east, the United Nations said. Their bodies were reportedly found on the road by other members of the convoy.
Pibor is the main town in Boma state, a vast underdeveloped territory bordering Ethiopia which was rocked by violence between competing clans earlier in March. The remote area is largely under government control but fought over by both sides in the conflict and plagued by militias and other armed groups.
Blow to humanitarian efforts
This attack is another blow to humanitarian efforts to help alleviate the suffering from war-induced famine.
"Some populations may not be met if aid workers decide it is unsafe to go to those areas," said Ian Ridley, head of the UN Office for the Coordination of Humanitarian Affairs in South Sudan.
"We need access and increasing security at the time of increasing needs," he added. "We are seeing the opposite at the moment."
Ridley called on the parties to cease hostilities and work for peace.
The African Union also strongly condemned the attack. "We are appealing to the government and all the stakeholders that they protect the humanitarian actors who are here to help the people of South Sudan," said AU Chairperson Moussa Faki Mahamat, who visited South Sudan's capital Juba on the weekend.
Who's to blame?
Rebel fighters loyal to former Vice President Riek Machar said the government should be held accountable as the killings took place on its territory.
"We don't have forces in that area. Instead it's the government forces and militias who control that area," said the spokesman for the rebel Sudan People's Liberation Movement (SPLM-IO) forces, Lam Paul Gabriel.
The government said it was too early to say who was behind Saturday's ambush.
The past two months have seen a sharp increase of attacks on humanitarian workers and their premises, "mirroring a rapid deterioration in the security and economic situation of the country," a statement from the United Nations Mission in South Sudan (UNMISS) said.
At least 79 aid workers have been killed since the start of the civil war in 2013.
The conflict between President Salva Kiir and his former deputy Machar has killed tens of thousands and displaced 3.4 million people. One million people are on the brink of famine.
Waakhe Simon Wudu contributed to this report.