The Democratic Republic of Congo has accused UN peacekeepers of failing to stop rebel troops killing civilians in the east of the country.
"People are being slaughtered and [UN peacekeepers] did nothing," a spokesman for President Joseph Kabila said.
The comments came as regional leaders met UN Secretary General Ban Ki-Moon in Kenya for crisis talks.
There were also reports that fresh fighting has broken out between rebels and government troops north of Goma.
Congolese rebels have been fighting government troops in eastern Congo since August, causing tens of thousands of civilians to flee.
The summit in Nairobi will be a diplomatic banging together of heads to avoid the fighting escalating into a regional conflict, says the BBC's Karen Allen.
Mr Ban's aim is to get a peace deal which was signed earlier this year back on track.
Rebel leader General Laurent Nkunda is not attending the talks, but he is in contact with the UN and other delegates at the summit.
'Killed by guns'
Congolese army General Vainqueur Mayala, the head of government forces in North Kivu province, told the Reuters news agency that there had been a "clash" between his troops and rebels loyal to Gen Nkunda near a refugee camp in Kibati on Friday.
Thousands fled towards Goma when the mortar and small arms fire broke out, a reporter for Agence France Presse said.
Meanwhile, the UN said it was investigating reports that rebels led by General Nkunda had killed civilians in their homes in the eastern town of Kiwanja.
At least 12 bodies were found in the town, which was retaken by rebels loyal to him earlier this week.
"They knocked on the doors, when the people opened, they killed them with their guns," said Simo Bramporiki, whose wife and child were killed during the night.
One woman showed journalists the bodies of five men inside her house, one of them her husband, and two more lying outside.
Gen Nkunda claimed his fighters, who have also seized control of the town of Nyanzale, about 80km (50 miles) north-west of Goma, had attacked armed pro-government militia.
However, reports say there was nothing to indicate the men, most of whom were wearing civilian clothing, were fighters.
A spokesman for the UN in DR Congo, Madnodje Mounoubai, told the BBC that the UN was doing its best to help civilians, but that peacekeepers could not fire at rebels when they were surrounded by civilians.
The Congolese government has refused to negotiate with Gen Nkunda, calling him a terrorist.
He says he is fighting to protect his Tutsi community from attack by Rwandan Hutu rebels, who fled to Congo after the 1994 genocide.
The Congolese government has often promised to stop Hutu forces from using its territory, but has not done so.
For its part, the Congolese government accuses Rwanda trying to destabilise it of by backing the rebels, which Rwanda denies.
Gen Nkunda also objects to government plans for foreign involvement in exploiting the country's vast mineral wealth.
Correspondents say a ceasefire around Goma appears to be holding, but the latest clashes have sparked fears the rebels could follow through on their threat to attack the city.
Tens of thousands of people have sought refuge there.
Meanwhile, Rwandan President Paul Kagame has blamed the international community for failing to address what he says are the root causes of the crisis, despite channelling tens of millions of dollars into the region.
He said the real reason for the crisis was what he described as the weak leadership of the Congolese government, which had failed to disarm Hutu rebels.