DAKAR, Senegal (AP) — A bomb at a refugee camp in eastern Congo has killed at least 5 people, including children, a spokesperson for the Congolese army said Friday.

Two children and their mother were among the dead, and more than 20 other people were injured, John Banyene, a civil society activist based in Goma, the provincial capital of North Kivu, told The Associated Press.

Lt Colonel Ndjike Kaiko, the army spokesperson, blamed the attack on the Mugunga refugee camp in North Kivu on a rebel group, known as M23, with alleged links to Rwanda, in a statement provided to the AP.

A military spokesman for the rebel group, Lt. Col. Willy Ngoma, denied any role and accused the army of planting the bomb.

M23 has seized more territory this week, capturing the mining town of Rubaya.

The town holds deposits of tantalum, which is extracted from coltan, a key component in the production of smartphones. It is among the minerals that was named earlier this month in a letter from Congo’s government questioning Apple about the tech company’s knowledge of “blood minerals” being smuggled in its supply chain.

The decades-long conflict in eastern Congo has produced one of the world’s worst humanitarian crises, with over 100 armed groups fighting in the region, most for land and control of mines with valuable minerals. Some are fighting to try to protect their communities.

Many groups are accused of carrying out mass killings, rapes and other human rights violations. The violence has displaced about 7 million people, many beyond the reach of aid.