The army of the Democratic Republic of Congo has effectively crushed a 20-month rebellion that threatened the government's hold on the country's mineral-rich eastern province, U.N. special envoy Martin Kobler says.

But lasting peace is likely to remain elusive because other rebel groups and criminal syndicates plundering the region's deposits of gold, diamonds, copper, cobalt and uranium still plague the region, a key battleground in Africa's deadliest and seemingly endless war.

Congolese officials say 10,000 refugees have fled into Uganda to flee a new rebel group named M18, about which little is known.

U.N. officials estimate there are still thousands of armed men prowling the eastern DRC, which remains a magnet for bandits, warlords, unscrupulous corporations and greedy neighbors.

The Congolese army, stiffened by a 3,000-strong U.N. intervention brigade, drove M23 out of its last stronghold into the hills along the Rwandan border in an offensive launched in late August.

After four days of fighting, the heaviest since August, Kobler reported to the U.N. Security Council: "It is practically the military end of the M23."

Ida Sawyer, a senior researcher with Human Rights Watch who was in the area Tuesday, reported M23 "has lost a huge amount of territory this last week.

"There's been a lot of defections. The top leadership may have already fled into Uganda or Rwanda."

The clashes centered around Kikumba, on a 6,000-foot-high plateau north of the regional mining hub of Goma, less than a week after peace talks in Kampala, Uganda, collapsed.

M23's reported defeat likely stems in part from international pressure on Rwanda, which the U.N. maintains has, along with Uganda, armed, funded and directed M23 for their own economic purposes.

Like a dozen other African states over the years, Rwanda and Uganda have repeatedly engaged in the Congolese conflict, lured in part by the DRC's treasure house of minerals.

Both countries have denied these accusations. But the U.S. global intelligence consultancy Stratfor noted Uganda "has supported the rebels in Congo because of its own economic interests across the border.

"For its part, Rwanda has traditionally backed Tutsi rebels in eastern Congo, including M23, because they contain the threat of Hutu rebels and help Kigali access eastern Congo mineral commodities."

Further, M23 is led by ethnic Tutsis. The 1994 genocide in Rwanda, in which the Hutu regime in Kigali slaughtered some 800,000 Tutsis, enflamed Congo's internal rifts.

That engulfed the DRC, formerly Zaire, in the deadliest conflict in African history in which some 5 million people have died from the fighting, disease and starvation.

After Rwanda's Hutu regime was toppled, more than 2 million Hutus fled to the Congo fearing reprisals by the new Tutsi-dominated regime.

Among them were many militiamen responsible for the genocide. They allied themselves with the regime in Kinshasa, the Congolese capital and began attacking the country's ethnic Tutsis.

Rwanda, which has an impressive military capability despite its small size, insists its national security is threatened, and has long accused Kinshasa of aiding Hutu extremists in the eastern DRC.

The late March formation of the U.N. combat brigade, made up of troops from South Africa, Tanzania and Malawi, with a mandate to engage and defeat the M23 rebels, was the game-changer in the rebellion. The ramshackle Congolese army had shown little inclination to tackle the rebellion.

The unusual combination of U.N. military muscle and international economic aid was what brought an end to the latest phase in the DRC conflict that dates back to the First Congo War of 1996-97 when Rwanda invaded what was then Zaire.

The fortunes of Rwanda, and its President Paul Kagame, took a tumble in 2012 when the patience of donor nations aiding Rwanda ran out, and they slashed aid that accounted for around 40 percent of Kigali's budget.

The United States, a major contributor, added its weight against Rwanda on Aug. 25, warning Kagame "to cease any and all support for M23."

M23 largely comprises fighters from a now-defunct rebel group which signed a peace pact with Kinshasa March 23, 2009. That opened the door for the rebels to join the DRC military.

In 2012, many M23 men defected from the DRC army, claiming Kinshasa had failed to implement the 2009 agreement, and went on the rampage.