Hundreds of Congolese have fled into Uganda following rebel attacks on their homes.
Officials in North Kivu province said M23 fighters stormed Tchanzu and Runyoni villages.
A Congolese army base was reportedly attacked.
Eyewitnesses say there has been fierce fighting between the rebels and government troops.
The M23, which is mainly made up of ethnic Tutsis, used to be a major fighting force in eastern DR Congo, seizing the regional capital Goma in 2012.
It later engaged in talks with the Congolese government but says its demands have never been met.
The UN had previously accused Uganda and Rwanda of supporting the M23 rebels.
BBC