KAMPALA, Uganda -- The presidents of Congo and Rwanda are meeting in Uganda Wednesday for emergency talks to stem growing tensions between the leaders and their nations, as a rebellion believed to be backed by Rwanda has taken over Congo's eastern provincial capital and its airport.

A top Ugandan diplomat with knowledge of the talks said Wednesday Rwandan President Paul Kagame and Congolese President Joseph Kabila met Tuesday night in the Ugandan capital, Kampala. He said Uganda's President Yoweri Museveni will mediate Wednesday talks.

The diplomat, who spoke on condition of anonymity because he was not authorized the discuss the meetings, said Kabila may be compelled to enter into direct negotiations with M23 rebels, who took control Tuesday of the strategic, eastern provincial capital of Goma and its airport. The Congolese government has said it would not negotiate with the rebels.

"We take it as an emergency meeting," the diplomat said of the talks. "President Kabila is the one who sought the meeting with President Kagame. Museveni had been pressing them to talk. We believe that this is the last chance to solve this thing. The time has come for Congo either to talk or fight (the rebels). You can't do both."

Rebels on Tuesday also pushed toward Bukavu, another provincial capital which lies to the south of Goma. As explosions rang out in the lakeside city of Goma, civilians ran down sidewalks looking for cover. Thousands of residents fled across the border to Rwanda, the much-smaller nation to the east.

By early afternoon the gunfire had stopped and M23 soldiers marched down the potholed main boulevards, unimpeded. Their senior commanders, who the United Nations has accused of grave crimes including recruiting child soldiers, summary executions and rape, paraded around the town in all-terrain vehicles, waving to the thousands of people who left their barricaded houses to see them.

The United Nations peacekeepers, known by their acronym MONUSCO, were not helping the government forces during Tuesday's battle because they do not have a mandate to engage the rebels, said Congolese military spokesman Olivier Hamuli, who expressed frustration over the lack of action by the peacekeepers.

A UN spokesman said in New York said that the nearly 1,500 UN peacekeepers in Goma held their fire to avoid triggering a battle. The peacekeepers "cannot substitute for the efforts of national forces" in Congo, said spokesman Eduardo del Buey.

On Wednesday the Security Council will review the mandate of the UN peacekeeping force in Congo. A resolution adopted Tuesday by the Security Council asks the UN secretary-general to recommend possible redeployment, and possible "additional force multipliers."

The resolution approved unanimously by the council imposes targeted sanctions, including a travel ban and assets freeze on the M23 rebel group leadership. But it did not name two countries accused by Congo of supporting the rebels: Rwanda and Uganda.

The council demanded that the M23 rebels withdraw from Goma, disarm and disband, and insisted on the restoration of the crumbing Congolese government authority in the country's turbulent East.

The resolution also calls for an immediate end to external support to the rebels and asks the UN secretary-general to report on the allegations of foreign support while expressing its readiness to take appropriate measures.

The rebels are believed to be backed by Rwanda, and to a smaller extent by Uganda, which are accused of equipping them with sophisticated arms, including night vision goggles and 120 mm mortars. Evidence is mounting of the involvement by the neighboring country and on Friday, the United Nations Group of Experts is expected to release its final report, detailing the role the neighboring nations played in the recruitment, financing and arming of the rebel movement, which was born in April.

Congolese government spokesman Lambert Mende said that Rwandan soldiers had crossed into Goma, hiking over footpaths across a volcano that looms between the two countries.

President Kabila arrived in Kampala on Tuesday afternoon, hours after Goma had fallen to the rebels. Uganda in recent times has led regional efforts -- under the auspices of the International Conference on the Great Lakes Region, or ICGLR-- to stem the crisis in eastern Congo. One of those meetings recently called for the creation of a "neutral international force" to police eastern Congo, to which the east African nation of Tanzania has already pledged troops. The force was to comprise at least 4,000 soldiers, but its mandate is not yet clear and money is said to be a problem.

Ugandan officials say the leaking of a report by a group of UN experts implicating Uganda in the Congo violence undermined those diplomatic efforts. Uganda denies supporting the rebels.