* UN official says powerless to stop rebels
* Fighting inflaming tension between Congo and Rwanda
* Refugees flee Goma camps, leaders due to meet for talks
* France calls for review of UN mandate
By Jonny Hogg
GOMA, Democratic Republic of Congo, Nov 20 (Reuters) - R ebels widely believed to be backed by Rwanda seized t he eastern Congolese town of Goma on Tuesday, parading past United Nations peacekeepers who gave up the battle for the frontier city of one million people.
As the leaders of Rwanda and the Democratic Republic of Congo were due to meet for crisis talks in Uganda, France called for a review of the local U.N. mandate, saying it was "absurd" that a substantial force, made up of troops from India, South Africa and Uruguay, had failed to hold off a few hundred rebels.
The rebel takeover of Goma came after days of clashes between the M23 movement and U.N.-backed Congolese soldiers that forced tens of thousands of residents to flee, raising fears of human rights abuses in the sprawling lakeside city.
The M23 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.
As night fell in the town, the capital of North Kivu province, gunfire had died down and the streets were largely deserted, apart from some rebel patrols on the streets.
The capture of Goma will be an embarrassment for Congo's President Joseph Kabila, who won re-election late last year in polls that provoked widespread riots. There were pockets of demonstrations against the fall of Goma in other towns.
A senior U.N. source told Reuters that international peacekeepers gave up defending Goma after the Congolese troops evacuated under pressure from the advancing rebels.
"There is no army left in the town, not a soul," he said, asking not to be named. "Once they were in the town, what could we do? It could have been very serious for the population."
But French Foreign Minister Laurent Fabius called for an overhaul of the mandate for MONUSCO, the U.N.'s Congo mission.
"MONUSCO is 17,000 soldiers, but sadly it was not in a position to prevent what happened. It is necessary that the MONUSCO mandate is reviewed," Fabius told reporters.
While conflict has simmered almost constantly in Congo's east in recent years, this is the first time Goma has fallen to rebels since foreign occupying armies officially pulled out under peace deals at the end of the most recent 1998-2003 war.
U.N. experts say Rwanda, a small but militarily capable neighbour that has intervened in Congo repeatedly over the past 18 years, is behind the revolt. Congo's mineral wealth, including diamonds, gold, copper and coltan - used in mobile phones - has inflamed the conflict and little has been spent on developing a country the size of Western Europe.
Hundreds of M23 fighters accompanied their leader Sultani Makenga into Goma, where they were greeted by cheering crowds shouting "welcome" and "thank you". Many in the town share ethnic and cultural ties with the rebels and with Rwanda.
Before the rebel force arrived, local people, many apparently drunk, had thrown up roadblocks of stones in the largely deserted streets pelted by heavy rain.
"We've taken the town, it's under control," said Colonel Vianney Kazarama, a spokesman for the rebels. "We're very tired, we're going to greet our friends now."
Analysts said it was unclear if M23 would try to make Goma a base for a push on the Congolese capital Kinshasa, 1,500 km (900 miles) away, as past rebellions have done, or would use the victory to demand the government open talks with its leaders.
"By making this demand, the M23 aimed to reduce the crisis to a domestic affair, thereby preventing Kinshasa from internationalising it in order to negotiate a solution at the regional level," the International Crisis Group said.
Sources at Uganda's presidency said Kabila was due to meet Rwandan President Paul Kagame in Kampala after Uganda's President Yoweri Museveni met the two leaders separately.
Uganda's Junior Foreign Affairs Minister Asuman Kiyingi told Reuters the rebels would not attend the talks.
Congo's government has rejected direct talks with the rebels, saying any dialogue must be with Rwanda, not the M23. "We will continue (resisting) until Rwanda has been pushed out of our country," Information Minister Lambert Mende said.
But Rwanda said Congo and its foreign backers have failed to address the root causes of the conflict.
"What happened today in Goma is a clear indication that the military option has failed to bring about a solution to this crisis and that political dialogue is the only way to resolve the ongoing conflict," the foreign ministry said.
Rwanda accused Congolese troops on Monday of shelling the Rwandan border town of Gisenyi, but it added it would not respond militarily to what it called Congo's "provocation".
Before M23 took the city, streams of residents crossed into Rwanda. More than 50,000 people who fled earlier fighting abandoned refugee camps around Goma, according to Oxfam.
"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.
The U.N. has about 6,700 peacekeeping troops in North Kivu, including some 1,400 troops in and around Goma, and the mission had previously promised to defend the town. It has used attack helicopters to repeatedly strike rebel advances south.
On Tuesday afternoon, armoured U.N. vehicles still rolled through the streets of Goma, offering help to residents, but troops did not try to block the rebels. No government soldiers were to be seen, with residents saying they left along the main road west toward Bukavu after the rebels began moving in.
The U.N. said on Tuesday its forces could not substitute the nation's security forces but said peacekeepers remained in control of the airport and would protect civilians.
Wars in the central African nation have killed about 5 million people in a decade and a half and many eastern areas are still afflicted by violence from a number of rebel groups, despite the decade-long peacekeeping mission.
While M23 has been accused of abuses in areas it controls, it has also set up an administration that tries to provide basic services such as healthcare, police training and garbage removal, residents have told Reuters.
M23 is led by members of a previous rebel movement who were brought into the Congolese army and then mutinied eight months ago, accusing the government of violating the deal. Many, however, believe they have since become a front for Rwanda.
Uganda has blamed the current upsurge in fighting on U.N. accusations that it was supporting rebels, a charge it denies.
"Uganda was mediating in this conflict ... and we had managed to restrain M23," Kiyingi said. "Then the U.N. 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."
Before taking Goma, the rebels controlled a string of towns to the north and east, near the borders with Uganda and Rwanda.
Congo analyst Jason Stearns said the fall of Goma would probably intensify international pressure on Rwanda, which has had aid cut due to the accusations it supporting Congo's rebels. But it may also now see an opportunity to exert its influence.
"Donors, and probably the Congolese government, will," Stearns said, "Have no choice but to deal with the rebels and call on Rwanda to help."