Police fired tear gas at demonstrators who threw molotov cocktails and chunks of masonry.

They ripped Kabila's campaign posters from signposts and set fire to banners in the streets of the capital, Kinshasa.

The country is tense ahead of Sunday's vote - the first free, multiparty elections for presidential and parliamentary positions for more than 40 years.

Kabila is believed to be the front-runner in a field of 33 candidates seeking to lead the vast central African nation out of a post-war transitional period.

The protesters, from two opposition parties, are demanding that the elections are delayed. They say election officials are using irregularities in the voters roll and the printing of five million spare ballot papers to rig the poll.

Electoral authorities have rejected the charges.

Many Congolese support Kabila for negotiating a settlement that ended five years of war triggered by his father, a former rebel leader who took power after his troops forced Mobutu Sese Seko out of the country in 1997.

National unity government

Kabila inherited the presidency in 2001 after his father was assassinated by a bodyguard and has led a national unity government overseeing a series of peace deals that ended the wars in 2002.

Aid groups say about four million Congolese died during the wars which involved six African countries, mostly of hunger or disease stemming from the violence.

The Democratic Republic of Congo remains poor despite its enormous mineral wealth and violence continues in the eastern borderlands near Rwanda and Uganda.

DR Congo has the world's largest
UN peacekeeping force

The largest United Nations peacekeeping force in the world is deployed in the country -17,000 troops have been there since 1999 and 2,000 EU soldiers have been sent to support them during the polls.

On Tuesday, the UN's World Food Program said recent fighting among militia groups and army in eastern Ituri Province had caused another 38,000 people to flee their homes.

The food agency said its food stocks were "being stretched to the breaking point" and needed $106 million to feed an estimated 1.7 million people across the country over the next year.

"The historic elections are attracting the world's attention but whatever the outcome, the need for food assistance will remain," said WFP's Congo country representative, Felix Bamezon.