Published: 2022-05-26 19:22:05 BdST
The army recaptured its base in Rumangabo, the area's largest, from the M23 but the rebels still appeared to control much of the surrounding area, said Emmanuel de Merode, director of the Virunga National Park, who is based in Rumangabo.
There was also heavy fighting overnight near the strategic town of Kibumba, about 20 km (12 miles) northeast of Goma, said de Merode.
An imam there said the town fell to the M23 on Wednesday.
"The army fell back, leaving the terrain to the M23. They are still there," the imam said.
Spokesmen for Congo's army could not be immediately reached for comment.
M23 spokesman Willy Ngoma told Reuters that the rebels had routed the army and allied militias, which he blamed for initiating hostilities.
Ngoma said the M23 was now satisfied and had "no ambition of taking territory and conquering and administering it." But when asked if the M23 might move on Goma, he added: "The day that will be necessary for our defence, we will not hesitate."
The M23 insurgency stems from the long fallout from the 1994 genocide in neighbouring Rwanda. The group's leadership is from the Tutsi ethnic group and has justified its attacks by saying it is battling the Democratic Forces for the Liberation of Rwanda (FDLR), a militia founded by ethnic Hutus who fled Rwanda after participating in the genocide.
In 2012, the M23 captured Goma, a city of more than 1 million people, before being chased by Congolese and UN forces into Rwanda and Uganda the following year.
Since then, M23 fighters, frustrated by the slow pace of a demobilisation process aimed at reintegrating them into civilian life if they lay down their weapons, have periodically returned from camps in those countries to stage attacks inside Congo.
In a statement late on Wednesday, Congo's government renewed accusations that Rwanda, which is led by President Paul Kagame, a Tutsi, was backing the M23.
Rwanda's government spokeswoman said she would respond shortly. Rwanda has in the past denied charges it backs the M23. The M23's Ngoma denied the group was receiving support from Rwanda.