Violence between the two communities also displaced some 350,000 in late 2017 and early 2018
Fighting has erupted again in the northeastern Ituri region of the Democratic Republic of Congo, the army said on Saturday.
The Congolese army said it lost three soldiers and killed 20 militiamen in the unrest overnight Friday to Saturday in the Djugu area.
Authorities say at least 160 civilians died in Ituri in June in clashes between militias.
On July 2, President Felix Tshisekedi announced a major military operation in the province's Djugu and Mahagi territories, with the offensive extending to South Kivu province to put a "definite end" to the dozens of militias roaming the lawless, mineral-rich region.
The UN refugee agency has said instability has forced more than 300,000 people to flee their homes, with people escaping unrest in Djugu territory especially.
Tens of thousands of people died in clashes between the Hema and Lendu ethnic groups between 1999 and 2003 in Ituri.
Violence between the two communities also displaced some 350,000 in late 2017 and early 2018.
In a separate development, it was announced that UN Secretary-General Antonio Guterres will visit Beni in North Kivu on September 1.
Ituri and North Kivu province, just to the south, are trying to roll back a major epidemic of Ebola that has claimed nearly 2,000 deaths since August 1, 2018.
Both provinces sit on DR Congo's eastern border with Uganda.
In this context, the army also added that Brigadier General Jacques Nduru had replaced Major-General Marce Mbangu Mashita Marcel after four years at the head of military operations in North Kivu.