M23 rebels have attacked army posts in Rutshuru territory near the border with Uganda and Rwanda, DRC national army spokesman Sylvain Ekenge said in a statement.
Fighting that erupted Thursday was still going on in some areas on Sunday but the situation was under control, Ekenge added.
A civil society source who did not wish to be named said the M23 had captured the village of Ntamugenga, a strategic target close to a highway connecting the city of Butembo to provincial capital Goma.
More than 23,000 people have fled the latest bout of fighting. Most come from Ntamugenga and the nearby town of Rutsiro, a humanitarian worker in Goma said.
Four civilians were killed and 40 injured, including children, the army spokesperson said.
M23 spokesman Willy Ngoma and the group's president Bertrand Bisimwa have both posted Twitter posts accusing the army of initiating the violence.
The M23 seized large swathes of territory during an insurrection in 2012 and 2013, before its fighters were chased out by Congolese and United Nations forces into Uganda and Rwanda.
There have been regional efforts in recent years to have the M23 demobilize, but its leaders have complained about the slow implementation of a peace accord and accused the DRC army of waging war against it.
Kinshasa accuses Rwanda and Uganda of backing the group, which they deny.
The M23 declared a ceasefire in April, and the seven countries of the East African Community trade bloc set up a regional military force to try to stem decades of .militant activity in eastern DRC.