Rebels believed to be backed by Rwanda have claimed control of Goma in the east of the Democratic Republic of Congo.
The fighters walked through the frontier city of about one million people on Tuesday, past UN peacekeepers who did nothing to stop them.
Fighters from the M23 group entered Goma following days of clashes with UN-backed Congolese soldiers that forced tens of thousands of residents to flee. A senior UN source told Reuters that international peacekeepers had given up defending the city after the Congolese troops evacuated.
The rebellion has aggravated tensions between Congo and its neighbour Rwanda, which Kinshasa's government says is orchestrating the insurgency as a means of grabbing the chaotic region's mineral wealth. Rwanda denies the assertion.
A Reuters witness saw the heavily armed rebels walking through the streets of the Goma, perched near Rwanda's border on the edge of Lake Kivu, past UN armoured vehicles and peacekeepers, who looked on.
"Despite the attack helicopters, despite the heavy weapons, the FARDC (Congo national army) has let the town fall into our hands," Colonel Vianney Kazarama, a spokesperson for M23 told Reuters by telephone.
He said the rebels had left a corridor open for Congolese forces to evacuate.
Goma's capture will be an embarrassment for President Joseph Kabila, who won re-election late last year in polls that triggered widespread riots in Kinshasa and which international observers said were marred by fraud.
The senior UN source told Reuters that international peacekeepers had been unable to mount a defence after Congolese troops evacuated.
"There is no army left in the town, not a soul ... once they were in the town what could we do? It could have been very serious for the population," he said asking not to be named
Streams of residents headed for the nearby border with Rwanda, saying they had been ordered to evacuate by the army. More than 50 000 people who fled fighting earlier this year have abandoned refugee camps around Goma.
"With the war, we're suffering so much, I've never seen anything like this in my life," a woman who gave her name only as Aisha told Reuters, clutching her three children.
M23 is led by mutinying soldiers who rose up eight months ago, contending that Congo's government violated a 2009 peace deal that was meant to integrate them into the army.
UN experts, however, support the view that Rwanda, which has intervened in Congo repeatedly over the last 18 years, is behind the revolt.
The vast Central African nation was shattered by wars between 1994 and 2003 that killed about five-million people. Many eastern areas are still plagued by violence from a variety of rebel groups, despite UN-backed efforts to defeat them.
The United Nations has about 6,700 peacekeeping troops in North Kivu, including some 1 400 troops in and around Goma.
Another neighbour of Congo, Uganda, blamed the escalation of fighting in eastern Congo on a leaked UN report that accused it and Rwanda of supporting Congolese rebels, a document Kampala said damaged its mediation efforts.
Uganda has vigorously denied the UN charges, which emerged in October, and Junior Foreign Affairs Minister Asuman Kiyingi said Kampala had been forced to retreat from its mediating role.
"Uganda was mediating in this conflict ... and we had managed to restrain M23," Kiyingi told Reuters.
"Then the UN comes up with these wild and baseless allegations against us and we decided to step aside and leave the situation to them and now you see the results," he said.
Uganda has threatened to pull its troops out of peacekeeping operations in Somalia unless the UN allegations are withdrawn. – Reuters