The United Nations has lodged a protest with Khartoum after a peacekeeping supply convoy in Darfur was ambushed by what the UN said were Sudanese troops.
The attack is the first against the new joint AU-UN peacekeeping force
A civilian Sudanese driver is in a critical condition after being shot seven times in the attack, the joint UN and African Union force, Unamid, said.
It said its peacekeepers had not fired back and there were no UN casualties.
UN Secretary-General Ban Ki-Moon condemned the strike "in the strongest terms".
The attack, which took place on Monday, is the first time the new peacekeeping operation has come under fire since the UN took over last week.
"Sudanese armed forces" fired upon the "clearly marked" convoy, said a spokeswoman for Mr Ban.
Some reports suggested the attackers may have been government soldiers who mistook the convoy for rebels.
The UN Secretary General called on the Sudanese government to "provide unequivocal guarantees that there will be no recurrence of such activities by its forces".
Khartoum has not commented on the incident.
The convoy had been carrying fuel and food to a joint United Nations-African Union outpost in the West of Darfur.
Tensions have been escalating in the area over the last few weeks.
There have been violent clashes between the Sudanese government and rebel groups.
Neighbouring Chad has been accused by Khartoum of bombing villages in the area, and each country accuses the other of sheltering rebel movements dedicated to overthrowing their respective regimes.
Unamid is due to become a 26,000-strong force but for the moment has just 9,000 troops.
At least 200,000 have been killed and two million forced from their homes in the five-year conflict.