– The M23 rebel group blamed for killing scores of civilians in eastern Congo over the last year and a half announced Tuesday it was ending its rebellion as an emboldened Congolese military seized the last two hills that had remained under rebel control.

While the dramatic developments marked a significant success in the Congolese government's fight against armed groups in the embattled east, experts warned that the rebel retreat would not result in an immediate peace in a region ravaged by fighting for nearly two decades.

U.S. envoy to Congo Russ Feingold welcomed the M23 announcement, saying it was a "critical and exciting step in the right direction."

In the capital, Congolese government spokesman Lambert Mende vowed that the military would now focus on pursuing Hutu fighters from the FDLR. The group is led by Rwandans who helped commit the 1994 genocide and later escaped to Congo, prompting a series of Tutsi rebellions, including the latest one by M23.

"M23 has been crossed off the list and now the military has its sights on the FDLR," Mende told journalists.

About 100 M23 fighters have been captured by government forces. M23 leader Sultani Makenga and other high-ranking officials within the movement are believed to have fled into neighboring Rwanda or Uganda, Mende said.

The announcement of M23's demise came after the Congolese military, backed by U.N. forces, stepped up its offensive against the rebels last month as peace talks once again stalled. The Congolese military rapidly seized control of more than a half-dozen towns in just a matter of days, and Mende said Tuesday they had finally recaptured the last two remaining rebel areas of Chanzu and Runyonyi.

M23 President Bertrand Bisimwa said in a statement early Tuesday that he was ordering rebel commanders to "prepare troops for the process of disarmament, demobilization and social reintegration on terms to be agreed upon with the Congolese government."

Careful optimism

Residents of Goma, a city of 1 million people that the M23 briefly overtook one year ago, expressed cautious optimism that the end of M23 could stabilize the area wracked by many rebel groups and militias.

"That they put down their arms and stopped fighting is a good thing. We are liberated but I'm not sure it's the end of the M23," said Diane Wamahoro, a 20-year-old waitress.

Ida Sawyer, a senior researcher with Human Rights Watch in eastern Congo, called the M23's declaration "a significant and positive step forward." The group has documented dozens of killing and rapes blamed on M23 since its formation last year.

"There are huge challenges ahead and one will be the arrests and bringing to justice of those responsible for serious abuses," she said.

Jason Stearns, a Congo expert, wrote on his blog Congo Siasa that the Congolese military had been performing better than it did in 2012 and also had benefited from the U.N. mission, which helped plan the latest operations against the rebels.

"But it may be the third factor that was the determining one — the absence of support from Rwanda," Stearns wrote. "According to several reports from the front lines, despite indications of some cross-border support in the Kibumba area, the M23 was largely left to its own devices."

M23 is widely believed to have received military and financial support from the government of neighboring Rwanda, whose president is also Tutsi. Rwanda denies having aided the rebels despite evidence laid out in a report by a United Nations group of experts. However, that support appears to have waned in recent months amid growing international pressure for it to stop fueling Congo's troubles with rebels.

In the aftermath of the Goma siege, internal divisions mounted within M23. The group was substantially weakened after its leader Bosco Ntaganda turned himself in to face charges at the International Criminal Court earlier this year.