The United Nations has accused government troops in the eastern Democratic Republic of Congo of raping civilians and looting villages.
A spokesman for the U.N. mission in Congo, Lieutenant Colonel Jean-Paul Dietrich, says the attacks took place Monday and Tuesday, and were centered around the Kanyabayonga area, north of the regional capital, Goma.
U.N.-funded Radio Okapi says the violence has caused panic in several villages and prompted many people to flee.
Also Tuesday, the United Nations said the Congolese army briefly exchanged fire with rebels just north of Goma.
U.N. Secretary-General Ban Ki-moon told reporters Tuesday he is "very concerned" about the reports of looting and rape.
The secretary-general said fighting between rebels and government forces in eastern Congo has cut off aid to at least 100,000 displaced people, north of Goma. He said their situation has grown "increasingly desperate."
Aid agencies and human rights groups have warned of a growing humanitarian crisis in North Kivu, where rebels led by renegade General Laurent Nkunda launched an offensive late last month.
Earlier Tuesday, Human Rights Watch said at least 50 civilians were killed in the rebel-held town of Kiwanja on November 4 and 5. It said the majority were killed by Nkunda's forces in reprisal against those believed to be enemy collaborators.
The World Food Program is pushing to feed the tens of thousands of people displaced by the recent fighting. The agency said Monday it had almost finished distributing 10-day food rations to 135,000 people in camps around Goma.
The WFP estimates the number of people in need of food aid across the eastern DRC to be more than 1.3 million. Many were displaced in previous bouts of fighting between Nkunda's forces and the government.
Nkunda formed his militia in 2004, saying he needed to protect minority Tutsis from Hutu fighters originally from Rwanda. The rebels and government began new clashes in August, following the collapse of a January peace deal.
Some information for this report was provided by AFP, AP and Reuters.