Witnesses said presidential guards, using tanks and heavy machine guns, opened fire around a house in the capital, Kinshasa, where United Nations officials and ambassadors were meeting Jean-Pierre Bemba who will face Kabila in a second-round vote for the presidency.
The UN mission chief for Congo, and ambassadors from a group of foreign donors were trapped in the building by the fighting outside but were then rescued by UN and European peacekeepers.
Bemba's spokesmen said heavily armed members of the presidential guard had attacked the candidate's followers around his riverside house, but the presidency said they had acted to deal with an armed threat to Kabila.
Richard Leon Kasonga, the army spokesman, appeared on national television and issued an order banning all troops from carrying their weapons in public without a written exemption. He appealed for calm, saying: "We're all members of the same army."
UN troops deployed
About 150 soldiers in 20 armoured personnel carriers from the 17,000-strong UN peacekeeping force have been sent to retrieve the foreign envoys from Bemba's home.
Jean-Tobias Okala, a UN spokesman, said:
"An operation has been launched to extract the ambassadors."
Smoke was seen rising from
Bemba's home in Kinshasa
Gun battles between soldiers loyal to Kabila and armed supporters of Bemba killed five people on Sunday, UN sources said.
The Congolese police and UN peacekeeping troops had been patrolling the half-deserted capital after Sunday's clashes which followed the announcement that the two men would face each other in a second-round vote on October 29.
Kabila, with 44.81% of the votes, finished well ahead of Bemba, who had 20.03%, but failed to gain more than 50% which was needed to win the presidency in the first round.