Demonstrators reportedly killed after car set ablaze and crowd tried to storm UN base in protest at lack of protection

United Nations troops have been accused of killing two civilians in eastern Democratic Republic of the Congo as the body's first offensive force is dragged into an escalating conflict.

On Saturday, scores of angry residents took to the streets, complaining that the UN had not done enough to protect them. A UN car was set ablaze and, when the crowd allegedly tried to storm a UN base, two protesters were killed.

Witnesses claim that UN troops from Uruguay opened fire on the demonstrators, but the Uruguayan president, Jose Mujica, denied this, insisting that they only fired rubber bullets and it was Congolese police who used live ammunition.

The UN has opened an investigation into the incident, which has the potential to embarrass the 3,000-strong "intervention brigade" that was created in March and entered combat last week against the M23 rebel movement.

Fighting broke out last Wednesday after weeks of relative calm in and around the eastern city of Goma. The UN troops shelled rebel positions on Thursday but the Congolese government soldiers they are supporting suffered heavy casualties over the weekend, according to an Associated Press report.

Dr Isaac Warwanamiza said he had seen 82 bodies since early on Sunday, 23 of whom he claimed were government troops, the highest death toll reported since hostilities broke out last week. "I'm overwhelmed by what I've seen: bodies blown apart, arms and feet here and there," he said.

Eight of the dead had no uniforms, 23 were government troops and the rest were M23 rebels, the doctor added. The total of wounded Congolese troops at the military hospital is 720, according to army chaplain Lea Masika. Two UN peace enforcers from South Africa and one from Tanzania have also been injured.

The front line of fighting is only nine miles north of Goma. The M23 rebels briefly held the strategic city in November last year and then retreated a few miles away. The Congolese army is yet to achieve its immediate objective of cutting off M23 from a border crossing where the rebel group is believed to receive supplies from neighbouring Rwanda.

On Sunday, the UK pulled its foreign office staff out of Goma due to security concerns.

The US state department said: "We urgently call on (Congolese) and Rwandan governments to exercise restraint to prevent military escalation of the conflict or any action that puts civilians at risk. We reiterate our call for Rwanda to cease any and all support to the M23." Rwanda has repeatedly denied UN allegations that it backs the M23 rebels.