"There were 11 people in the vehicle and seven died immediately, while another died this morning," Norwegian Church Aid said.
Rebels of the Lord's Resistance Army (LRA) were believed to have carried out the attack, the group said.
All those killed in the ambush, which happened on Thursday morning close to Parajok near the Ugandan border, cooperated in helping refugees and displaced people in southern Sudan.
Two of them were workers from Norwegian Church Aid, named as Kenyan Simon Kenyatta and Sudanese nurse Esther Mania. The other workers also were from church-linked aid groups -- one from Africa Inland Church, three from Episcopal churches in Sudan.
The other two were from the Sudanese Relief and Rehabilitation Association, the humanitarian arm of the Sudanese People's Liberation Army (SPLA) rebel group.
Relations between Sudan and Uganda have been strained for years with both countries accusing each other of helping rebels fighting their respective governments.
Sudan has for years accused Uganda of giving sanctuary to the SPLA, the main rebel group in the mainly Christian and animist south. Uganda says Sudan harbours LRA rebels.
Norwegian Church Aid supports the SPLA.
Talks at ending Sudan's 17-year civil war resume on Saturday with little optimism of a settlement to a conflict which has killed more than 1.5 people.
- Reuters - Thomson Reuters Foundation
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