U.N. Secretary-General Ban Ki-moon has condemned in the strongest possible terms an attack on a United Nations-African Union supply convoy in Sudan's western Darfur region.

U.N. officials have reported that a civilian driver was critically wounded when the convoy was attacked by elements of the Sudanese army as it traveled between Umm Baru and Tine in western Darfur late Monday.

Officials say the convoy was clearly marked and was carrying rations for UNAMID personnel in the region.

In a statement Tuesday Secretary-General Ban says that for the joint AU - U.N. peacekeeping operation to perform its functions, the government of Sudan must provide unequivocal guarantees that such action will not occur again.

The secretary-general says the United Nations is lodging a protest with the government of Sudan.

The U.N. says the convoy driver was shot seven times and is in critical condition. It says U.N. troops did not return fire and the incident is still under investigation.

Separately, President Bush says he has asked the new special U.S. envoy to Sudan Ambassador Richard Williamson to advance efforts to end violence in Darfur.

Mr. Bush said in a statement Tuesday that he is committed to the rapid deployment of an effective peacekeeping force along with serious dialogue to help end the crisis in Darfur.