Former Prime Minister Kengo Wa Dondo has announced he will support ex-rebel leader Jean-Pierre Bemba in DR Congo's second round election run-off.
Joseph Kabila (l) faces Jean-Pierre Bemba (r) in the 29 October polls
Kengo Wa Dondo who served under former President Mobutu Sese Seko is the latest politician to back Mr Bemba.
Violent clashes are continuing ahead of the 29 October poll between Mr Bemba and the incumbent Joseph Kabila, the UN mission in DR Congo (Monuc) says.
The elections are the first fully democratic polls to be held since 1960.
Most of the politicians who have been active in DR Congo's recent political history are now under the umbrella of Mr Bemba's Union for the Nation (UN), the BBC's Arnaud Zajtman in Kinshasa says.
"I have managed to get support on behalf of Mr Bemba from political players originating from all the provinces of this country," Mr Kengo told the BBC.
"The coming vote will be an ethnic vote," he added.
As well as Mr Kengo, Mr Bemba has the support of the daughter of Congo's first president as well as several other famous politicians.
Meanwhile Mr Kabila has secured alliances with some political players who did well in the first round of elections.
These include 80-year-old Antoine Gizenga and Nzanga Mobutu - son of the ex-president.
Mr Kabila gained 45% of the vote in July, against 20% for Mr Bemba.
About 30 people were killed in subsequent clashes between rival supporters.
The Congolese had not had a free vote since 1960
The situation has since improved although incidents are still taking place between supporters of rival candidates, Monuc's human rights director, Fernando Castagnone, told the BBC Focus on Africa programme.
Mbuji-Mayi, Kindu and Lubumbashi have seen disputes such as armed groups taking away or destroying banners, he said.
Mr Kabila won a landslide in the Swahili-speaking, war-ravaged east, where he is praised for bringing peace.
However, many in the Lingala-speaking west doubt Mr Kabila's Congolese nationality and voted for Mr Bemba.
Our reporter says that deals among the politicans may not decide who wins though, as ethnic allegiances may hold more sway.
In which case, he says it remains difficult to determine who will win.
The second round will conclude the country's first fully democratic polls since independence in 1960.