Government troops in the Democratic Republic of Congo backed by United Nations soldiers suffered heavy casualties over the weekend, a doctor near the front line said. The news comes as they fought to push back M23 rebels who remained entrenched Monday just north of the eastern provincial capital of Goma. Dr. Isaac Warwanamiza told The Associated Press he had seen 82 bodies since early Sunday, 23 of whom he claimed were government soldiers, the highest death toll reported since hostilities broke out last week. The M23 rebels briefly held the strategic city of 1 million in November last year and then retreated a few miles away. Congolese and U.N. troops have been battling to dislodge rebels from heights overlooking the city since Wednesday. The United States State Department has condemned the actions of the M23, calling on the rebel group to immediately cease hostilities, disarm and disband. The U.S. also suggested that Rwanda is assisting the rebels. Meanwhile, the UN has opened an investigation into reports that its troops killed two Congolese civilians during protests in the eastern city of Goma on Saturday, amid fighting with rebels. Eyewitnesses said the two died when a crowd tried to storm a UN base and said troops from Uruguay had opened fire. Many Congolese accuse the 18,000-strong UN mission in the Democratic Republic of Congo of not doing enough to end two decades of conflict in the east of the country.