(Adds confirmation that Sudanese government forces attacked, U.N. secretary-general's reaction)

By Andrew Heavens

KHARTOUM, Jan 8 (Reuters) - Sudanese soldiers opened fire on a U.N./African Union supply convoy in Sudan's war-torn Darfur region, the first attack on the newly formed joint peacekeeping mission, the United Nations said on Tuesday.

A spokeswoman for U.N. Secretary-General Ban Ki-moon said in a statement that "elements of the Sudanese armed forces" attacked a clearly marked convoy from the UN/AU Mission in Darfur (UNAMID) late on Monday.

A diplomatic source in the region told Reuters the soldiers apparently confused the peacekeepers for rebels. No one was immediately available for comment from Sudan's armed forces.

One civilian Sudanese driver was in a critical condition after being shot seven times, UNAMID said in a statement. Its forces were now at a "high state of alert" in Darfur.

"The secretary-general condemns this attack in the strongest possible terms," spokeswoman Michel Montas said, adding that Khartoum "has to provide unequivocal guarantees that there will be no recurrence of such activities by its forces."

She said the United Nations would lodge a formal protest with the Sudanese government.

Details of the attack remained unclear.

"The convoy was traveling ... in the dark," the diplomat in Darfur said. "They could have mistaken them for rebels. There have been a lot of things going on in that area recently."

UNAMID said the convoy was taking food and fuel to a UNAMID outpost near the town of Tine close to the border of western Darfur state and Chad.

"A UNAMID Supplies convoy was attacked last night, 7 January 2008, at approximately 2200 Hrs (1900 GMT), on its way from Umm Baru to Tine in Western Darfur.

"The road convoy was on a re-supply mission to UNAMID team sites in the area between Um Baru, Tine and Kulbus, an area which has witnessed violent clashes between the government of Sudan and rebel movements and where UNAMID air operations have been restricted due to the security concerns."

It added that a diesel truck and a UNAMID armed personnel carrier were damaged in the attack.

UNAMID troops guarding the convoy had not returned fire and none were injured, said the statement.

"The UNAMID leadership is in direct consultations and discussion with Sudanese authorities in Khartoum and El Fasher (capital of north Darfur region and UNAMID's headquarters) over the matter," it said.

TENSIONS RISE

The attack came at a time of heightened tension in west Darfur state and neighboring regions in Chad. Chadian air force planes bombed Chadian rebel positions close to the west Darfur's capital el Geneina on Sunday, a U.N. report said of the second reported incursion into Sudanese territory in two weeks.

Sudan and Chad accuse each other of sheltering rebel movements dedicated to overthrowing their respective regimes.

Darfur rebel group the Justice and Equality Movement (JEM) on Sunday said it had occupied the town of Tanjeki, close to el Geneina, and shot down a government Antonov aircraft. Local media later printed government denials of the JEM attacks.

The "hybrid" force of AU and U.N. troops replaced a struggling AU mission in Darfur on January 1. The plan is for it ultimately to comprise 20,000 soldiers and 6,000 police, but only a little over a third of those are so far in place.

U.N. Secretary-General Ban Ki-moon has warned the existing peacekeeping force was too small to deal with the deteriorating situation. He has also expressed "serious concern" about the recent surge in violence in western Darfur and eastern Chad.

International experts estimate 200,000 people have died since mostly non-Arab rebels took up arms in early 2003 accusing central government of neglecting the remote region.

Khartoum mobilized mostly Arab militias to quell the revolt, which has created what aid agencies say is one of the world's worst humanitarian crises. Khartoum accuses The western media of exaggerating the conflict. (Additional reporting by Louis Charbonneau at United Nations) (Editing by Keith Weir and Bill Trott)

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