A peace initiative launched at the weekend by Olusegun Obasanjo, the UN envoy and former Nigerian president, is aimed at ending weeks of renewed fighting in North Kivu, which has displaced a quarter of a million civilians.
'Heavy weapons fire'
Obasanjo has also met Joseph Kabila, the Congolese president, and his Rwandan counterpart Paul Kagame in a bid to stop the conflict from escalating into a repeat of a 1998-2003 Congo war that killed several million people.
A UN peacekeeper at Rwindi, who declined to be identified, told the Reuters news agency Nkunda's National Congress for the Defence of the People (CNDP) forces had started advancing against government troops on Sunday.
"At 7pm, there was firing from both sides ... small-arms fire and long range heavy calibre weapons passing over our base in both directions ... By morning, the CNDP was here," he said.
The road into Rwindi was littered with military boots and blankets.
In the town, a ranger post for the Virunga National Park, rebel fighters manned checkpoints abandoned by the army.
To the north, sporadic gunshots rang out that peacekeepers said were probably fired by hungry soldiers poaching animals.
"Both sides were shooting for hours. The children were traumatised ... The UN soldiers were hiding in their trenches but we had to remain outside," said Clement Augustin Kasabuni, 33.
"There were more than 100 bombs that fell last night. What kind of ceasefire is that?" he asked.
Nkunda is demanding direct talks with Kabila on Congo's future, something the president has so far refused to grant.
A Congolese official told Reuters on Monday Kabila's government would only negotiate with the rebel leader if he agreed to return to a January peace deal he abandoned on the grounds it was one-sided and manipulated by the government.
A UN official said the retreating Congolese government soldiers at Rwindi destroyed ammunition and a rocket launcher by setting them on fire, causing explosions and rockets to fire in the direction of UN peacekeepers, wounding one.
Rebels have collected large amounts of military hardware abandoned by the weak and chaotic Congolese army.
On Monday, a military court sentenced four government soldiers to life imprisonment for looting.
One of them was found guilty of war crimes, including rape and looting, in a court-martial open to the public in the capital of Nord-Kivu province.
Three other men were convicted of abandoning their posts in time of war and misuse of weapons during looting, while a fifth was given a six-month sentence for shooting and wounding a civilian.
The defendants went on the rampage while they were guarding the home of the regional Congolese military commander, General Vainqueur Mayala.
Three other soldiers also accused of looting were acquitted.
Both the Congolese army and the rebels have been accused of war crimes and other acts of violence against civilians.