Gunmen have attacked a United Nations-African Union police patrol in Sudan's Darfur region, about two kilometers north of a refugee camp.

A spokesman for the U.N.-AU mission says four gunmen stopped the unarmed patrol near the Zam Zam camp on Wednesday and beat one of the officers with an AK-47 rifle. He said the gunmen also stole identification cards and two vehicles, one of which has since been recovered by Sudanese police.

U.N. Secretary-General Ban Ki-moon has condemned the attack, and called on the Sudanese government and rebel forces to allow U.N.-AU peacekeepers to fulfill their mission.

Meanwhile, Sudan's President Omar al-Bashir has turned down an invitation to attend a U.N. Security Council meeting aimed at improving cooperation with regional groups, such as the AU.

Sudanese officials say Mr. Bashir received only short notice of the April 17 meeting, and already had plans.

The invitation was issued by South Africa, which presides over the Security Council this month. Other countries invited to the meeting include Sudan's neighbors Chad and the Central African Republic.

Diplomats say Mr. Bashir's presence at the meeting could have sparked protests from groups that monitor the conflict in Darfur.

Critics say Mr. Bashir has obstructed the full deployment of the U.N.-AU peacekeeping force. Nine-thousand peacekeepers are already on the ground, but plans call for another 17,000.

Five years of fighting in Darfur between rebels, the Sudanese government and government-backed militias has killed an estimated 200,000 people and displaced some 2.5 million others.

Some information for this report was provided by AFP.