The UN said that rebel general Laurent Nkunda's National Congress for the Defence of the People (CNDP) clashed Tuesday and Wednesday with the pro-government Mai-Mai militia.
The CNDP then forced thousands of civilians out of Kiwanja, northeastern DR Congo under the pretext of searching for remaining militia, a BBC correspondent in the town said.
Aid agencies say that renewed fighting between the CNDP and government forces has displaced at least 250,000 people since late August.
As many as 50,000 of these people fled during four days of fighting last week, many of them to in and around Goma, the capital of the North Kivu province.
The CNDP called a ceasefire last Wednesday after it routed the Congolese army and came on the verge of taking Goma, but aid agencies are warning of a humanitarian catastrophe.
The UN refugee agency, UNHCR, which on Wednesday began a "massive food distribution" to displaced North Kivu, warned that the fresh fighting could jeopardise the delivery of aid.
The ceasefire around Goma has held despite the new clashes, which the Congolese army deny any involvement in.
A regional summit on the conflict aimed at cementing the ceasefire is to take place in Kenyan capital Nairobi Friday.
The presidents of DR Congo and Rwanda, Joseph Kabila and Paul Kagame, are to attend the summit, as is United Nations Secretary General Ban Ki-moon.
Western diplomats feel that bringing Rwanda and the DR Congo together at the table is key to resolving the conflict.
DR Congo has accused Rwanda of backing Nkunda, who says he is fighting to protect Tutsis from armed Hutu groups. Many Hutus fled to DR Congo after the 1994 massacres in Rwanda, when Hutu militants killed an estimated 800,000 Tutsis and moderate Hutus in the space of a few months.
However, many analysts say that the ethnic dimension of the conflict is just a smokescreen for militias to grab a slice of DR Congo's rich mineral deposits.
Nkunda has said that he is ready to take Goma and also continue onto the capital of DR Congo, Kinshasa.
However, the UN peacekeeping mission has vowed to defend Goma.
The Under-Secretary-General of Peacekeeping Alain LeRoy said Wednesday that the DR Congo peacekeeping mission (MONUC) was reinforcing its positions in North Kivu, particularly in Goma.
However, while MONUC backed up the Congolese army during the CNDP offensive it was unable to hold back the rebel tide.
MONUC chief Alan Doss said last week that his troops, numbering 17,000 across the whole of the sprawling central African nation, were stretched to their limit by the conflict.
Calls for more UN troops to be deployed in the country have so far not been answered with any firm commitments, although a UN Security Council meeting to approve the deployment of another 3,000 troops is mooted for late November.
More than 5 million people are estimated to have died as a result of the 1998-2003 war in the resource-rich nation, most of them from hunger and disease.
The conflict is often referred to as the African World War, owing to the large number of different armed forces involved. dpa ml ds
- Deutsche Presse Agentur
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