GOMA, Congo (AP) -- A rebel group created just seven months ago seized the strategic provincial capital of Goma, home to more than 1 million people in eastern Congo, and its international airport on Tuesday, according to a rebel spokesman and witnesses.

Explosions and machine-gun fire rocked the lakeside city as the M23 rebels pushed forward on two fronts: toward the city center and along the road that leads to Bukavu, another provincial capital which lies to the south. Civilians ran down sidewalks looking for cover and children shouted in alarm. A man clutched a thermos as he ran.

By early afternoon the gunfire had stopped and M23 soldiers who are believed to be backed by Rwanda, marched down the potholed main boulevards, unimpeded. Their senior commanders 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.

"MONUSCO is keeping its defensive positions. They do not have the mandate to fight the M23. Unfortunately, the M23 did not obey the MONUSCO warnings and went past their positions (at the airport). We ask that the MONUSCO do more," he said.

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

On Tuesday, 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.

"Goma is in the process of being occupied by Rwanda," said Mende, speaking from Congo's distant capital of Kinshasa. "We have people who saw the Rwandan army traverse our frontier at the Nyamuragira volcano. They have occupied the airport and they are shooting inside the town. Our army is trying to riposte but this poses an enormous problem for them _ this is an urban center where hundreds of thousands of people live," he said.

A Congolese colonel, who was at the frontline in Goma before the city fell, said that the soldiers he saw were Rwandan. Neither his claim nor Mende's could be independently verified.

M23 rebel spokesman Col. Vianney Kazarama confirmed that they had taken the airport and the city. "We are now inside the city of Goma," he said.

Goma, a city of low-lying buildings, many topped by rusted corrugated roofs, was last threatened by rebels in 2008 when fighters from the now-defunct National Congress for the Defense of the People, or CNDP, stopped just short of the city. Their backs to the wall, the Congolese government agreed to enter into talks with the CNDP and a year later, on March 23, 2009, a peace deal was negotiated calling for the CNDP to put down their arms in return for being integrated into the national army.

The peace deal fell apart this April, when up to 700 soldiers, most of them ex-CNDP members, defected from the army, claiming that the Congolese government had failed to uphold their end of the deal. They charged that they were not properly paid and equipped and that the government has systematically discriminated against ethnic Tutsis, which make-up the majority of their ranks.

Although M23 is tapping in to long-held grievances regarding the marginalization of Tutsis in Congo, analysts and country experts say the real reason for the rebellion is over control of Congo's vast mineral riches, a good chunk of which is concentrated in North Kivu province, where Goma is located, as well as neighboring South Kivu, of which Bukavu is the capital.

Germany, which is a member of the U.N. Security Council, called on the rebels to halt their military action immediately. Foreign Minister Guido Westerwelle said in a statement that he called on Congo's neighbors, a reference to Rwanda and Uganda which are accused of backing M23, to not do anything to worsen the crisis.  "I expect of Congo's neighboring states that they refrain from doing anything which further exacerbates the situation," Westerwelle said.

Over the weekend, U.N. Secretary-General Ban Ki-Moon called Rwandan President Paul Kagame and asked him to call the M23 leaders and ask them to stop their advance, according to a statement issued at U.N. headquarters in New York. In January, Rwanda will assume a seat on the United Nations Security Council, creating a diplomatic minefield in light of what is happening in Goma.

If the rebels succeed in taking Bukavu, it will mark the biggest gain in rebel territory since at least 2003, when Congo's last war with its neighbors ended.

Jean-Claude Bampa, who lives near the road to Sake, the first town on the drive to Bukavu, spoke on the telephone over loud gunfire in the background.  "I can hear gunshots everywhere, it is all around my home," he said on Tuesday morning. "We are stuck inside and are terrified. I pray this will be over soon."