Major Dieudonne Kasereka, the army's spokesman in South Kivu province, said a unit of reinforcements came under attack while travelling though the village of Kagogo in Uvira district on Tuesday morning.

The assailants were "militiamen of the Makanika-Twigwaneho coalition," he said referring to an armed group claiming to represent the Banyamulenge -- Congolese Tutsis of Rwandan heritage.

"In the exchange of fire, the army killed 18 militiamen," while two soldiers died and five were seriously wounded, he said.

More than 120 armed groups are active in eastern Democratic Republic of Congo, according to monitors, many of them a legacy of regional wars that raged in the 1990s.

The Makanika-Twigwaneho are led by an army colonel, Michel Rukundo Makanika, who deserted in early 2020 and set up a force in the Fizi highlands of South Kivu.

The area is the site of long-running feuds over land and resources between the Banyamulenge on one side and the Bembe, Fuliro and Nyindu groups on the other.

Clashes between Banyamulenge combatants and the Congolese army have increased in recent months.

On December 28, a colonel and three soldiers, as well as 12 militiamen, were killed.