The clashes have taken place in Ituri province, where in separate conflicts, the army is battling the Allied Democratic Forces (ADF) -- a group with suspected links to the so-called Islamic State -- and an ethnic-based militia called CODECO.

On Thursday, nine civilians in the Mambembe area were "massacred" by the ADF, and three more were killed in an attack on Saturday, the area's chief, Janvier Musoki Kinyongo, told AFP.

"People have fled my area. ADF rebels are moving about the region," he said.

In another part of Ituri, soldiers killed seven ADF operatives and captured one in an offensive launched on Highway 4, about 90 kilometres (55 miles) south of provincial capital Bunia, army spokesman Jules Ngongo said.

Separately, the army said it had carried out a "helicopter-backed operation" against CODECO in Ituri's territory of Djugi.

"Thirty-one CODECO militia elements (were) neutralised and several were wounded, it said.

The Cooperative for the Development of the Congo (CODECO) is a military-religious sect that claims to represent the Lendu ethnic group, which has a historic feud with the Hema community.

Fighting between the two groups flared between 1999 and 2003, claiming tens of thousands of lives before being quelled by a European Union peacekeeping force, Artemis.

Violence then resumed in 2017, blamed on the emergence of CODECO.

Since October, CODECO has stepped up attacks in the Djugu area, bordering Lake Albert and Uganda which lie to the east.

On Saturday, a suicide attack at a crowded nightspot in Beni, in neighbouring North Kivu province, claimed seven lives.

North Kivu is the epicentre of ADF attacks that, according to the Catholic Church, have claimed some 6,000 deaths since 2013. The group has also been blamed for a string of attacks on Ugandan soil this year.

On November 30, the DRC and Uganda launched a joint operation against the ADF.

The ADF is historically a Ugandan rebel coalition that established itself in eastern DRC in 1995, becoming the deadliest of scores of outlawed forces in the troubled region.

The Islamic State group presents the ADF as its regional branch -- the Islamic State Central Africa Province, or ISCAP.

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