KIBATI, Congo (Reuters) - Rwandan troops crossed into eastern Congo on Tuesday in a joint military operation by the Great Lakes neighbors to disarm Rwandan Hutu rebels seen as a root cause of more than a decade of conflict.
Both governments presented the operation as a move to finally pacify the east of Democratic Republic of Congo, where fighting flared again late last year during an advance by Tutsi insurgents who are sworn enemies of the mostly Hutu Democratic Forces for the Liberation of Rwanda (FDLR).
Analysts said allowing the Rwandan forces in was a risky strategy for Congolese President Joseph Kabila, whose government army has often been accused by critics of using the FDLR to fight armed opponents and keep Tutsi-led Rwanda at bay.
The European Union, however, called the operation a tangible sign of improved relations between the two countries.
The presence of the FDLR, who finance themselves by exploiting illegal mines in the mineral-rich east, triggered two previous Rwandan invasions of Congo that led to a wider 1998-2003 conflict. It also helped cause a 2004 rebellion by Congolese Tutsi rebels who went on the offensive in October.
Diplomats and U.N. peacekeepers said that up to 2,000 Rwandan troops crossed the border into eastern Congo on Tuesday under a December joint accord to act against the FDLR.
"The operations are beginning. We have invited Rwandan officers with their security contingents for their safety. They are observers," Congo's Information Minister Lambert Mende said.
He added the operations to disarm FDLR fighters were planned to last 10 to 15 days and would be restricted to North and South Kivu provinces, where an estimated 6,000 FDLR fighters roam.
The size of the Rwandan deployment appeared, however, to be more than a simple mission by "observers."
A Reuters reporter saw hundreds of Rwandan troops, wearing Rwandan flag patches on their uniforms and carrying mortars, rocket launchers and AK-47s, moving into Congo in the Kibati area north of the North Kivu provincial capital Goma.
Independent Congo analyst Jason Stearns said the joint operation marked a turning point in Kinshasa's attitude toward the conflict in the east. "It appears Kabila's government has decided to turn on what has been an ally, the FDLR," he said.
Rwanda's Information Minister, Louise Mushikiwabo, said the Rwandan forces would operate under Congolese command.
"This is a result of recent intense and sincere efforts -- diplomatic, military and other ... to bring peace and stability to the region," she told Reuters by text message.
U.N. peacekeepers also confirmed the Rwandan deployment.
"This morning between 1,500 and 2,000 RDF (Rwanda Defence Forces) crossed the border in the Munigi-Kibati zone," said Lieutenant-Colonel Jean-Paul Dietrich, U.N. military spokesman.
Dietrich said heavily armed Congolese army forces were also on the move and called moves to block movements by peacekeepers to monitor developments "unacceptable."
Experts said the FDLR guerrillas ensconced in the hills and forests of the Kivus could be a tough nut to crack militarily.
"These kinds of counter-insurgency operations are very difficult and always carry with them the risk of serious harm to the civilian population," Stearns said.
The latest Rwandan foray follows a Ugandan-led offensive against Ugandan LRA rebels in Orientale province to the north, and highlights Kabila's failure to make good on promises to pacify the volatile east after winning 2006 elections.
"Look where we are, two years after elections, the Rwandan army back in Congo and the Ugandans are back in Congo ... and the Congolese get screwed again," said one veteran foreign Congo analyst, who asked not to be named.
The analyst recalled Congo's 1998-2003 war, when Rwanda and Uganda backed rival rebel groups.
But EU Aid Commissioner Louis Michel was more optimistic. "It (the operation) highlights efforts to find a regional solution to the conflict in Congo," he said in a statement.
The presence in eastern Congo of Rwandan Hutu FDLR rebels, many of whom participated in Rwanda's 1994 genocide, has been at the heart of more than a decade of bloodshed.
The 1998-2003 war sucked in the armies of half a dozen nearby countries, and triggered a conflict-driven humanitarian catastrophe that killed an estimated 5.4 million people.
Rwanda and Congo have agreed on several past occasions to cooperate to tackle the Hutu rebels, but have failed to carry this out amid accusations that ill-disciplined Congolese government forces have sided with the FDLR Hutu fighters.
Additional reporting by Joe Bavier in Kinshasa, Hereward Holland in Kigali and David Lewis in Dakar; writing by Alistair Thomson and Pascal Fletcher, editing by Mark Trevelyan