Aid agencies say the “shocking” killing of six aid workers in South Sudan on Saturday is causing them to re-assess how and when they can deliver supplies.
The victims were ambushed by unknown attackers when travelling between Juba and the town of Pibor to the northwest.
Oxfam said the attack “demonstrates how dangerous it is here” and was leading agencies to re-evaluate “what is mission-critical and what is not”.
Aid deliveries would continue but could be delayed, it said.
The latest fatal attack on humanitarian workers came a month after famine was declared in parts of South Sudan.
The UN says the famine – the first to be announced anywhere in the world in six years – is man-made, resulting from a political conflict that escalated into war in 2013.
Oxfam humanitarian campaigns manager Dorothy Sang, who is in South Sudan, told the BBC it was “one of the most difficult countries to operate in right now”.
She said attacks on aid workers “unfortunately aren’t uncommon” – 12 have been killed this year alone and there have been a number of other, non-fatal attacks on aid convoys and warehouses.
She said Oxfam would continue delivering aid but was reassessing how this could be done with least risk.
Transporting aid by road was now “extremely dangerous” and agencies were considering whether they could step up transportation by air, and whether risks on the road could be reduced by aid organisations travelling in convoy.
This re-evaluation of risks could mean that aid deliveries were delayed, Ms Sang said.
“The brutal killing… has sent shockwaves through us all,” said Care International country director Fred McCray. “It is unacceptable that those trying to alleviate the suffering… are attacked for what they do.”