Fighters from Democratic Republic of Congo's M23 rebel group launched an offensive in eastern North Kivu province last week, spurring fresh fighting with the army in which four civilians were killed, the army said late on Sunday.
The unrest broke months of relative calm in east Congo following clashes between the army and M23 militants at the end of March.
The group 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 Congo's mineral-rich east.
But M23 rebels attacked army posts in Rutshuru territory near the border with Uganda and Rwanda on Thursday, the spokesman for the military governor of North Kivu, Sylvain Ekenge Bomusa Efomi, said in a statement.
Fighting was still going on in some areas on Sunday but the situation was under control, he added.
Four civilians were killed and 40 injured, including children, he said.
M23 spokesman Willy Ngoma and the group's president Bertrand Bisimwa have both posted Twitter posts accusing the army of initiating the violence.
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.
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 Congolese army of waging war against it.
Congo accuses Rwanda and Uganda of backing the group, which they deny.
(Reporting by Sonia Rolley; Writing by Sofia Christensen)
