Government troops in the Democratic Republic of Congo say they have gained more ground against M23 rebels as the head of the UN mission in the country described the movement as finished.

"Practically all M23 positions were abandoned yesterday, except for a small triangle at the Rwandan border," Martin Kobler told the UN Security Council on Monday, according to diplomats.

He said that the M23 had abandoned a key position on Mount Hehu near the Rwandan border, reportedly adding: "It is practically the military end of the M23."

An international force acting under a UN mandate have been aiding the government forces in DR Congo. A Tanzanian UN soldier was killed in the fighting on Sunday, but the rebels were rolled back and local civilians were overjoyed, Kobler said, according to officials present at the closed meeting.

Troops seized back control of a major military base at Rumanagabo, which lies about 40km north of Goma, the strategic capital of embattled North Kivu province, Lieutenant-Colonel Olivier Hamuli told the AFP news agency.

"We fought, but not for very long - the enemy is demoralised by the strength of firepower," Hamuli said on the fourth day of an offensive against the M23, following the suspension of peace talks in Uganda.

Troops recaptured two other towns, Kiwanja and Rutshuru, at the weekend and heavy fighting was reported at Kibumba, around 25km from Goma, where soldiers cleaning up the area made the grim discovery of three mass graves.

Graves found

One witness who did not give his name reported seeing "horrible things" at the site of the graves.

"I saw three or four child skulls, underwear and women's clothing. There were insects in some places, which meant there were not just bones there.

"Further on there was a large ravine where people said quite a lot of bodies had been thrown but I wasn't able to check," the witness said.

A special commission has been tasked with "identifying the graves" and  "determining their scale as well as those responsible for these serious human rights violations", the Congolese defence minister Alexandre Luba Ntambo said.

Ntambo said there was "no limit" to army action to drive out rebels. The M23 group was "a rebel movement, a negative force... I don't see how someone can stand up and tell us when to stop", he said.

Source: Agencies