The Congolese army said Wednesday it had killed 20 fighters from the M23 militia group and lost two soldiers in clashes with the rebels since the end of January.
General Leon Mushale told reporters in the eastern city of Goma that a further 25 rebels either were captured or surrendered and that six soldiers had been injured.
The clashes occurred in the eastern part of DR Congo, on and near the border with Uganda, on January 31 and also on February 20 to 22, according to the army.
Mushale, who heads military operations in North Kivu province, said the rebels fled "some to Uganda, others to Rwanda".
M23 is a mostly ethnic Tutsi rebel group that mutinied against the Democratic Republic of Congo in 2012, saying a peace accord signed in 2009 had not been respected by the government.
The militia was defeated the following year, and hundreds of fighters fled the country.
But in January, the Congolese government and numerous witnesses said former M23 rebels were spotted in the North Kivu village of Rutshuru, having crossed over from neighbouring Uganda.
The group still poses a threat to peace and security in the east of DRC, said UN peacekeeping mission MONUSCO, adding it has received "many signs" that former fighters remain.
DR Congo's resource-rich east has suffered nearly two decades of brutal conflict, with neighbouring states backing rebel groups in a civil war against Kinshasa's authority, and roaming armed militia triggering the mass flight of terrorised civilians.