The UN Security Council has extended an arms embargo against armed groups in Congo, strongly condemning a rebel group believed to be backed by Rwanda for attacking civilians.

In a resolution adopted unanimously on Wednesday, the council extended sanctions against armed groups in Congo until Feb. 1, 2014, and said it will consider additional measures against leaders of the M23 rebel group and those providing support to them.

Rebels started retreating from the territory they seized last week and pulled out of Masisi, their military leader said Wednesday, in the first concrete sign that international pressures have stemmed the advance of the fighters.

The M23 rebel group is made up of hundreds of officers who deserted the Congolese army in April. Since then, the rebels have occupied vast swaths of territory in mineral-rich eastern Congo. The rebels accuse Congo's government of failing to honour the terms of a 2009 peace deal that incorporated them into the national army.

The rebels took the provincial capital of Goma, and other nearby towns in eastern Congo without much of a battle last week, as the Congolese army fled in disarray and UN peacekeepers held fire.

A group of leaders for countries neighbouring Congo called for M23 to retreat no later than Friday to 20 kilometres outside of Goma.

Gen. Sultani Makenga, the military chief of the eight-month-old rebellion, said his fighters intend to abide by an ultimatum issued by the nations neighbouring Congo that called for the M23 rebels to retreat no later than Friday to 20 kilometres outside of Goma, the major eastern city that fell to the fighters eight days ago. He said he had ordered his fighters to retreat along the southeastern axis from Masisi to Goma, and they will then leave Goma via the northern route to Rutshuru.

"My soldiers began to retreat from Masisi yesterday [Tuesday]. We will go via Goma and then after that we will retreat to 20 kilometres past Goma toward Rutshuru," Makenga told The Associated Press on Friday. "I think that by Friday we will be able to complete this."

Congo's government spokesman Lambert Mende, who is based in the country's capital over 1,600 kilometres to the west, confirmed it had received reports of troops pulling out of Masisi.

"Yes, there are reports of movements [of their fighters out of Masisi] but we won't label it a retreat until it's over. They have played this game with us before, where they say they are moving and then find a reason not to," Mende said. "There will be no negotiations with Congo until they are 20 kilometres outside the Goma city limit."

In Goma, there was skepticism over the rebels' claim and confusion, after the leader of M23's political wing insisted that the fighters were not leaving the city of one million that is the economic heart of one of Congo's mineral-rich regions.

M23 vice-minister of the interior Theophile Ruremesha told The Associated Press on Wednesday that Congolese President Joseph Kabila's government needs to meet their wide-ranging demands for them to leave the city.

"Kabila has to meet our demands if we are to pull out," he said.

"For humanitarian reasons we cannot leave the town in the hands of just anybody," he said. "Creating the neutral force will take some time."

Pulling out from Goma would be a reversal of the statement by the M23's political chief Tuesday that the rebels would fight the government army to retain control of Goma.

The rebels seized Goma last week. The regional bloc demanded the M23 withdraw from the city by midnight Monday night, but the rebels defied the order.

Goma residents fear more fighting

Some Goma residents fear M23, which is only eight months old but already has a record of carrying out executions and forcing children into its ranks. But other residents of this sprawling, lakeside city of one million are afraid of the undisciplined Congolese army, which the rebels pushed out of Goma on Nov. 20. Dozens of people came out for an anti-Kabila rally, holding placards and pieces of cardboard decrying the distant government's inept handling of the conflict.

"I want Kabila to leave because he hasn't helped the people and our country hasn't moved forward since he came to power," said one of the marchers, Augustin Katombo. "I think M23 should stay because we don't want the army to come back."

M23 leader Jean-Marie Runiga says the rebel group has a large new cache of 1,000 tonnes of weapons, including heavy artillery, that were abandoned by the fleeing Congo army last week. (James Akena/Reuters)

About 1,500 UN peacekeepers were in Goma when M23 attacked on Nov. 20 and government forces fled, but the well-armed UN forces did not intervene, saying they lacked the mandate to do so. One of their main missions is to protect civilians.

Many people expressed anxiety about a possible attack by the Congo army, which lies in wait several dozen kilometres to the south of Goma.

"This is a nerve-racking situation. It fluctuates every hour and we cannot even plan for tomorrow," said Goma resident Ernest Mugisho. "The M23 needs to give a clear message because for us, the population, this is not good."

The rebel group has a large new cache of 1,000 tonnes of weapons, including heavy artillery, that were abandoned by the fleeing Congo army last week, according to M23 president Jean-Marie Runiga. Six flatbed trucks carrying crates of ammunition were seen Tuesday being driven by M23 soldiers north from Goma.

A UN group of experts said in a detailed report last week that M23 is backed by neighbouring Rwanda, which has provided them with battalions of fighters and sophisticated equipment such as night-vision goggles.

With files from CBC News