The Congolese army said it made significant advances against eastern rebel forces in a second day of fierce fighting on Saturday and called on neighbouring Rwanda to help disarm the insurgents.
The army clashed with M23 rebels on Friday for the first time in two months after peace talks in Uganda broke down this week. Rwanda accused the army of firing a shell into its territory, sparking fears its military might intervene.
M23 said in a statement on Saturday that the army had launched a "generalized attack" on several fronts but that the fighting was turning in its favour.
Army spokesman Colonel Olivier Hamuli said, however, that M23 had been forced out of Kibumba, a town 20 km (13 miles) north of Goma, the largest city in eastern Democratic Republic of Congo.
"We have pushed M23 into the hills on the Rwandan border," he told a Reuters reporter near the front line. "We now call on Rwanda to help us disarm their fighters."
Hamuli said the army was also advancing from Rwindi, north of M23-controlled territory in Congo's North Kivu province, attacking the rebel group in a pincher movement.
U.N. investigators have accused Rwanda of supporting M23, charges that Kigali denies.
M23 formed in early 2012 when army soldiers mutinied, saying the government had broken a 2009 peace deal signed with a previous Rwanda-backed rebel movement.
On Friday, Rwanda said shells fired by the Congolese army landed in its territory. Rwanda's U.N. ambassador told a closed-door meeting of the Security Council it would not tolerate such shelling and could respond militarily, diplomats said.
The fighting is the most serious since late August, when the Congolese army and a new U.N. Intervention Brigade forced M23 from positions just north of Goma. The brigade, made up mostly of South African and Tanzanian soldiers, has a mandate to take on and destroy armed groups in eastern Congo.
On-and-off peace talks between the government and M23, taking place in the Ugandan capital, Kampala, since December, stalled on Monday, with the government saying it would not offer rebel leaders a blanket amnesty.
The U.N. peacekeeping mission in Congo, MONUSCO, said on Friday it was on high alert and monitoring the clashes. MONUSCO aircraft flew over the region, but South African and Tanzanian troops present near the front line did not join the combat.
A U.N. spokesman in New York said some 5,000 civilians had fled across the border into Rwanda.