People gather around a tank abandoned by fleeing Congolese army in Ndosho near Goma.

DR Congo rebels on Thursday rejected international calls to pull out of the strategic eastern city of Goma, demanding peace talks with President Joseph Kabila before ending an offensive that has stoked fears of a wider conflict and humanitarian catastrophe.

“There must first be a dialogue with President Kabila,” one of the leaders of the M23, Jean-Marie Runiga Lugerero, told AFP by telephone two days after they took Goma. “There must be dialogue and solutions before anything takes place.”

As alarm grows in the international community about the unrest in the war-blighted central African nation, Kabila and his rival Rwandan counterpart Paul Kagame are due to meet at a regional summit on the crisis on Saturday in Uganda.

The United Nations accused the M23 rebels of carrying out summary executions in their sweep across the east and again charged that both Rwanda and Uganda were backing the group, whose chain of command is believed to include wanted war crimes suspect Bosco Ntaganda.

Rwanda and Uganda deny the charges.

The M23 rebels, fresh from their easy capture of Goma on Tuesday, claimed on Wednesday to have seized another nearby town and threatened to march all the way to the capital Kinshasa, about 1,500 kilometres (950 miles) away.

“We are not going to stop at Goma, we will go as far as Bukavu, Kisangani and Kinshasa,” M23 spokesman Vianney Kazarama told a crowd at a stadium in the lakeside city, also demanding that Kabila stand down.

Rebels said they had also seized Sake, about 20 kilometres northwest of Goma - the capital of the mineral-rich North Kivu region - and vowed to press on southwards to Bukavu, the other major city on the border with Rwanda.

But at talks in Kampala on Wednesday, Kabila and the leaders of Rwanda and Uganda insisted that the mainly ethnic Tutsi rebels must immediately pull out of Goma.

Kagame and President Yoweri Museveni of Uganda “made it clear that even if there were legitimate grievances by the mutinying group known as M23, they cannot accept the expansion of this war,” said a joint statement issued after the talks.

The United States also renewed calls for M23 to halt their latest offensive in a deeply troubled and impoverished country, the largest in central Africa.

“We want to see them immediately withdraw from Goma and cease any further advances and permanently disband,” State Department deputy spokesman Mark Toner told journalists. “We condemn any and all outside support of M23, any military assistance to the rebels in violation to the UN arms embargo.”

UN envoy Roger Meece accused the rebels of carrying out “summary executions” of local leaders in their advance on Goma and said they were trying to set up “a formal administrative or governing structure” in the region.

“The M23 forces are well provisioned and well supplied with uniforms and a variety of arms and ammunitions, many of which have clearly not come from existing FARDC (government army) stocks,” he told the Security Council.

A Security Council resolution Tuesday called for wider sanctions against M23 leaders and condemned all external support for the rebels.

The United Nations and other humanitarian groups have reported killings, abductions, looting and extortion of civilians and fears of a humanitarian catastrophe were growing as electricity and water supplies dried up.

Violent demonstrations reportedly erupted in several towns Wednesday, with some protesters targeting UN missions after rebels took over Goma facing little or no resistance from UN peacekeepers and the regular DR Congo army.

DR Congo Prime Minister Augustin Matata Ponyio said Kinshasa had “lost the battle but not the war”, and insisted the country's territorial integrity was “non-negotiable”.

The UN defended its peacekeepers after Goma fell, with a spokesman saying a battle for the city would have endangered civilians.

It has around 1,500 “quick reaction” peacekeepers in Goma, part of some 6,700 troops in North Kivu province, backing government forces against the rebels.

UN chief Ban Ki-moon issued a new condemnation of “grave” human rights violations by the fighters, although retreating government troops have themselves been accused of looting.

Rebels have been blamed for hundreds of deaths since the M23 mutinied in April after the failure of a 2009 peace deal that integrated them into the regular army.

Tens of thousands of people have fled their homes or camps around Goma, where the clean water supply and electricity supplies were cut.

Aid group Oxfam described the situation as “a humanitarian catastrophe on a massive scale”.

The International Criminal Court called for the urgent arrest of Ntaganda, a former army general nicknamed the “Terminator”, and Sylvestre Mudacumura, the commander of the FDLR, a Hutu militia group.

Both men are wanted on suspicion of war crimes and crimes against humanity in DR Congo.

Two wars that shook the whole of DR Congo in 1996 and 1997, and then again from 1998 to 2002, both began in the Kivu region, with Rwanda and Uganda playing active roles in both conflicts.

Since 1998, more than three million people are estimated to have died from combat, disease and hunger, and 1.6 million have been left homeless.

The former Belgian colony remains one of the world's least developed countries despite a wealth of cobalt, copper, coltan, diamonds and gold. - AFP