The Democratic Republic of Congo armed forces say they have won a "great victory" and are now in full control of the eastern town of Mushake.
The government sent thousands of troops east for the offensive
Army head Gen Dieudonne Kayembe said 50 rebels loyal to the rebel Gen Laurent Nkunda were killed, for the loss of four of his own men.
There is no word on Gen Nkunda's whereabouts but his forces are believed to have gone to the nearby mountains.
Meanwhile, the US, Burundi, Rwanda and Uganda have pledged to help DR Congo.
At a regional meeting in Ethiopia, they said they would strengthen the Congolese security institutions.
They also pledged not to "harbour negative forces".
This is seen as reference to Gen Nkunda, who Rwanda is accused of backing. Rwanda denies the claims.
It also means the Rwandan Hutu rebels in eastern DR Congo, which are at the heart of the region's instability.
Gen Nkunda says he cannot disarm while they are around; Rwanda has twice invaded DR Congo to stop them staging attacks.
Recent fighting in eastern DR Congo has displaced some 200,000 people, the UN says.
Gen Kayembe said the 82nd brigade of the Congolese armed forces had also taken control of all the high ground around Mushake, which will give his men a strategic advantage as the town overlooks a key road in the region.
The BBC's Arnaud Zajtman entered the town with the victorious government forces, who were accused of going on a drunken looting spree after their victory.
However, Jason Stearns, an independent DR Congo analyst based in Nairobi said the army should not get too carried away.
"A military victory is not a matter of taking a couple of towns," he told the Reuters news agency.
"This is guerrilla warfare - it's a matter of inflicting sustained damage. We haven't seen anything like that."
The UN mission in DR Congo (Monuc) has been providing logistical support to the Congolese armed force (FARDC) and on Tuesday said that as a last resort it would also "provide fire support" against the rebels.
The 15,000 UN soldiers in DR Congo are tasked with securing peace after a five-year conflict officially ended in 2002.
But a Monuc spokesman said mandate included supporting the legal authorities "with all necessary measures against any attempt by illegal armed groups to jeopardise the political process".