The UN's World Food Program says one of its Sudanese aid delivery drivers has been shot dead in South Kordofan state, one of two rebel-held border areas of Sudan where half a million people face potential famine.
The UN agency said two unknown assailants opened fire on a marked UN vehicle, killing Jamal Al Fadil Farag Allah. Another WFP staff member was wounded and airlifted to Khartoum.
An unnamed rebel spokesman quoted by the news agency AFP said the road where the shooting happened should have been under the control of Sudanese government forces.
Oil processing rig at Heglig in Sudan
Tensions between Sudan and South Sudan focus on oil
Saturday's incident, which was disclosed by the WFP on Sunday, coincided with a deal in which Sudan agreed on oil transit fees for crude exports from landlocked South Sudan, which was created last year.
On Sunday, a Sudanese negotiator at African Union-led talks in Ethiopia, said Khartoum had agreed to allow humanitarian aid into parts of Kordofan and neighboring Blue Nile state on the condition that hostilities involving rebels of the Sudan People's Liberation Movement-North (SPLM-N) cease "for a length of time."
Obeid added that aid would be distributed by three organizations but only under strict Sudanese supervision.
The SPLM-N insurgents fought alongside southern rebels during Sudan's 22-year civil war, which culminated in South Sudan's independence last year.
The European Union's foreign policy chief Catherine Ashton urged both Khartoum and the SPLM-N to follow a cessation of hostilities with political negotiations.