They said the attackers swooped around 3:00 am (0100 GMT) on a convoy of eight jeeps and fled when police escorting the vehicles opened fire, wounding some of the assailants.

Two jeeps carrying nearly 1,000 ballot papers were burned in the attack, AFP correspondents said.

Afterward residents of the area showed an AFP photographer presidential ballots that they said had already been marked when they found them.

Separately, bursts of gunfire were heard in the city around midday (1100 GMT) causing panic in Njanja district, with people running for cover.

It was not immediately clear where the shots were coming from or why. The shooting continued around 1130 GMT, though with less frequency.

An ex-member of a Katanga separatist group fighting for the province's independence told AFP the group had carried out the ambush on the election convoy.

"We want a self-determination referendum, and not this vote that doesn't have anything to do with us in Katanga," the self-described lieutenant Chana Kazi said by phone from South Africa.

He also claimed a Sunday attack by gunmen who raided a military camp and arms depot in the city, killing one person and fleeing after exchanging gunfire with soldiers.

Lubumbashi, the restive capital of the mining province of Katanga, had been a flashpoint of political violence in the run-up to Monday's elections.

Earlier this month, two days of street fights between opposition and government supporters shut down parts of the city. Banks and other businesses closed amid unrest in which shop windows were shattered and pedestrians mugged.

On Sunday, gunmen attacked a military camp and arms depot in the city, killing one and fleeing after exchanging gunfire with soldiers.

Provincial authorities said they had arrested three of the attackers, suspected of being separatist militants fighting for the province's independence.

By SAPA