Fresh fighting has broken out between rebel forces and the internationally-backed Congo military. The UN Security Council demanded an end to foreign support for the rebels, who are moving towards the city of Goma.
Rebel fighters captured the town of Kibumba on Saturday, despite strikes from UN attack helicopters who are assisting the Congolese military.
The fall of Kibumba means rebel forces are closer than they have ever been to Goma, the capital of North Kivu province, since a rebellion exploded eight months ago in the country's eastern provinces. The town lies north of Goma.
"Kibumba has fallen into the hands of the M23," said a spokesman for the UN Department of Peacekeeping Operations in an email.
M23 was founded earlier this year by former rebels who had been integrated into the army in 2009, but mutinied after they claimed the government failed to uphold its end of their agreement.
"Latest reports indicate that the FARDC (Congo's army) and MONUSCO (UN) forces are attempting to hold off a possible M23 advance toward Goma at Kibati, some 20 kilometers (12.4 miles) north of Goma," added the spokesman.
The UN said it moved in attack helicopters to strike rebel forces after civilians were forced to flee the area. The UN mission in Congo has a mandate to protect civilians and support the military dating back to 1999. No casualty figures have been reported yet by either side.
Alleged Rwandan involvement
North Kivu Governor Julien Paluku said the army had retreated to the south after M23 rebels advanced with the help of neighboring Rwanda. A Congolese government statement estimated that 3,500 Rwandans had crossed the border.
Rwanda denied the allegations, and called on the Congolese military and rebels to stop the violence, as shells were landing in its territory.
"We are not in a position to confirm direct Rwandan involvement in the M23 attacks," said the UN spokesman. "However, we are very concerned by reports that the M23 attacking forces appear to be well-equipped and supplied."
The spokesman added that UN Secretary General Ban Ki-moon had spoken to Rwandan President Paul Kagame, expressing his support for Congo and Kagame, urging the latter to "use his influence on the M23 to help calm the situation and restrain the M23 from continuing their attack."
During an emergency meeting of the UN Security Council on Saturday, the organization demanded an end to foreign support for M23. The council also said it would order more sanctions against the rebels and those who break the UN sanctions and arms embargos against Congo.
The unrest inside the country has displaced at least 390,000 people since April, and the UN warned in September that number could double in the coming months. A further 60,000 people have fled to Rwanda, according to the UN.
More than 5 million people are estimated to have died due to violence, hunger and disease in wars in Congo since 1998, making it the deadliest war since the Second World War.
There are approximately 6,700 MONUSCO forces in North Kivu province, with some 1,400 in Goma and the surrounding area, according to UN officials.
dr/jr (AFP, dpa, Reuters, AP)