Heavy fighting erupted in eastern Congo on Sunday, hours before former Nigerian President Olusegun Obasanjo, a United Nations peace envoy, was due to meet rebel leader Laurent Nkunda, the UN and witnesses said.
It was not immediately clear who was involved in the clashes. Artillery, rocket and small arms fire have been heard since early morning near the village of Ndeko, about 110 km (70 miles) north of Goma, the capital of North Kivu province.
Obasanjo is due to meet Nkunda later on Sunday morning, some 60 km southeast of Ndeko, in his efforts to end weeks of clashes between Nkunda's rebels and the army. The violence has sparked a displaced 250,000 some people, creating a humanitarian disaster.
"There is a lot of fighting going on. They are using heavy weapons -- rockets and artillery -- as well as small arms," a witness told Reuters from the road just south of Ndeko.
The UN peacekeeping mission also confirmed the clashes.
"We have had a flash report of heavy fighting since seven this morning (5 GMT) at Ndeko. We have sent a patrol out to see what is going on," said spokesman Lt-Col Jean-Paul Dietrich.
Neither the UN nor the witness could confirm who was involved in Sunday's clashes but Nkunda's fighters have previously clashed with both government soldiers and Rwandan Hutu rebels, known as the FDLR, in the area.
Nkunda accuses Congolese President Joseph Kabila of arming and using the FDLR to fight alongside his weak and chaotic army units. Kabila, meanwhile, accuses neighbouring Rwanda of supporting Nkunda's four year rebellion.
Nkunda initially took up arms saying he was fighting to defend fellow Tutsis in Congo from attack by the FDLR but, after marching to the gates of Goma last month, he is now calling for direct negotiations with the president.
Kabila has so far refused and there are fears that fighting could degenerate into a conflict similar to Congo's 1998-2003 war, which sucked in six neighbouring armies and killed over five million people, mostly from hunger and disease.