KINSHASA (Reuters) - Congolese President Joseph Kabila's guards fought gun battles with forces loyal to election challenger Jean-Pierre Bemba in the capital Kinshasa on Sunday, after poll results showed the two would have to enter a run-off.

Figures in from all but one constituency in the huge Democratic Republic of Congo showed the post-war vote was headed for a runoff between Kabila and Bemba.

But shooting in the tense capital, in which one person was reported killed, forced the Independent Electoral Commission (CEI) to abandon a planned results ceremony at its press centre as gun battles raged a few hundred metres (yards) away.

"There is a lot of confusion but some of Bemba's protection detail appear to have clashed with the presidential guard," said a senior official with the United Nations force.

White U.N. armoured personnel carriers (APCs) deployed as gunfire and heavier explosions echoed through the city centre.

Government spokesman Henri Mova Sakanyi accused Bemba's forces of starting the fighting, some of which took place near the headquarters of Bemba's MLC party.

"Bemba's soldiers started shooting at policemen. We don't known what the reason is. Maybe they were trying to block publication of the election result," he said.

He said three policemen had been wounded.

But Bemba's MLC party, which sprang from the Ugandan-backed rebel force he led in the war, accused Kabila's Republican Guard of attacking its headquarters in the city on Sunday afternoon.

"The Republican Guard started shooting at us for no reason. They killed one of our men," an MLC spokesman told Reuters.

VOTE GOES TO RUNOFF

Electoral commission head Apollinaire Malu Malu had been due to announce full provisional results at the CEI press centre at 8 p.m. (2000 GMT), but was forced by the fighting to cancel.

Later Malu Malu left aboard an APC, in a convoy of 13 U.N. armoured vehicles and armed Congolese police in pickups, to go to the state television studio to announce the results on air.

With ballots in from 168 of the vast country's 169 constituencies, Kabila led with 44.5 percent -- under the 50 percent level needed for a first-round win, according to calculations by election experts.

Bemba trailed in second place with more than 20 percent, meaning he will face Kabila in a run-off vote provisionally scheduled for October 29.

Antoine Gizenga, a veteran opposition politician in his 80s, is running in third place with 13 percent of the votes according to the latest results. Provisional results will still need to be confirmed by the Supreme Court.

"We have heard that there will be a second round but want to be reassured by an official statement," said Papa Antoine, an unemployed Kinshasa resident in 30s planning to watch on TV.

The July 30 presidential and parliamentary elections were the first free, open polls for more than 40 years and are meant to offer the huge country a fresh start after a decade of violence driven partly by greed for its mineral riches.

The world's largest peacekeeping force -- 17,000 U.N. peacekeepers, backed by more than 1,000 European soldiers -- is overseeing a peace process culminating in polls that cost $450 million and presented huge logistical and security problems.

Voting passed relatively smoothly, with millions voting peacefully despite insecurity in the east, where rebels still roam, and threats of unrest in towns hostile to Kabila.

But the vote has highlighted a split between Kabila's native Swahili-speaking east, which voted heavily for the 35-year-old president, and the Lingala-speaking west which rejected him, including the teeming city of Kinshasa where Kabila is disliked and seen by many as a foreign-backed stooge.