KHARTOUM, Sudan -- Sudanese soldiers shot at a convoy of U.N. peacekeepers in Darfur, critically wounding a local driver and wrecking a fuel tanker barely a week into the force's new mission in the region, U.N. officials said Tuesday.

The attack was the latest challenge for the U.N. force, which has been heralded by the international community as having the best chance to quell five years of violence in Darfur but took the field with only a fraction of the anticipated troops.

The United Nations condemned the attack, which occurred late Monday, and said it had protested to the Sudanese government that "a clearly marked [U.N.] supplies convoy was attacked by elements of the Sudanese Armed Forces while on its way from Um Baru to Tine in West Darfur."

A Sudanese working as a driver was hit by seven bullets, a tanker truck was destroyed and an armored personnel carrier was damaged, the U.N. said. The South African peacekeepers protecting the convoy did not return fire, and U.N. troops suffered no casualties, officials said.

"The government of Sudan has to provide unequivocal guarantees that there will be no recurrence of such activities by its forces," the U.N. said in a sharply worded statement.

There was no immediate comment by Sudan's government.

Mistaken identification

A U.N. peacekeeper in Darfur said Sudanese troops apparently mistook the U.N. convoy for Darfur rebels who operate in the area near the border with Chad. "It was night time, it seems the [Sudanese] soldiers lost their calm," he said.

A senior official with the U.N. peacekeeping mission, known as UNAMID, said the Sudanese soldiers stopped shooting after 10 minutes and let the peacekeepers go.

Both the peacekeeper and the official agreed to discuss the incident only if they were not quoted by name, because they were not authorized to give details to journalists.

U.N. vehicles are painted white and marked with the U.N. logo to signal their neutrality. It was unclear how the Sudanese soldiers could have mistaken them for rebels, who usually drive camouflaged pickup trucks and don't have armored vehicles.

The head of the peacekeeping mission, Rodolphe Adada, consulted with Sudan's Foreign Ministry on Tuesday and both sides "agreed to launch an urgent investigation," UNAMID spokesman Noureddine Mezni said.

"The is the first time UNAMID is attacked, and we hope it will be the last," Mezni said. "We are in Darfur to bring peace, not to fight."

The assault came amid escalating clashes along Sudan's border with Chad. Both governments have accused each other of supporting rebel movements in the two nations.

Sudan's government has been accused of using a militia of Arab nomads known as the janjaweed as a proxy force in its brutal fight with rebel groups based in Darfur's ethnic African farming communities -- a claim denied by the Khartoum regime.

More than 200,000 people have died since ethnic African groups rebelled in 2003 over accusations that the Arab-dominated national government discriminates against them. Some 2.5 million people have fled to refugee camps.

The U.N. peacekeeping mission that began Jan. 1 is the latest international attempt to end the violence. A poorly equipped African Union force of about 7,000 soldiers was unable to end the chaos and suffered dozens of casualties of its own.

The new joint U.N.-AU force, which incorporates the African peacekeepers, currently stands at about 9,000 soldiers and police officers and is supposed to grow to 26,000. The deployment is far behind schedule and Western countries have failed to commit heavy fighting equipment such as attack helicopters.

Sudanese President Omar al-Bashir long opposed any U.N. peacekeeping force in Darfur. Facing heavy international pressure, he agreed last June to allow the joint U.N.-AU force, but U.N. officials say his government has thrown up numerous bureaucratic obstacles to its deployment and powers.