At least two United Nations (UN) peacekeepers were killed and 13 others injured when their unit was ambushed by suspected rebels in eastern parts of the Democratic Republic of the Congo (DRC).

The Tanzanian unit was attacked early on Tuesday with four peacekeepers going missing, said the spokesman for the UN secretary general in a statement released later in the day.

Local administrator Amisi Kalonda stated that Ugandan rebels of the Allied Democratic Forces and National Army for the Liberation of Uganda (ADF-NALU) were responsible for the attack, which took place around Oicha area some 20 kilometers (12 miles) north of the city of Beni in North Kivu province, bordering the countries of Uganda and Rwanda.

Martin Kobler, the head of the United Nations Organization Stabilization Mission in the Democratic Republic of the Congo(or MONUSCO, which is initials of its French name "Mission de l'Organisation des Nations unies pour la stabilisation en République démocratique du Congo") posted a message on his Twitter account saying, "I cannot tolerate the repeated attacks on the Blue Helmets in the region of Beni, "pledging that the UN force would conduct "robust offensive operations."

The deadly attack came a day after a helicopter carrying the mission’s force commander in the region came under fire from unknown armed men.

This is while Army spokesman Victor Masandi reported on Monday that at least 16 rebels and four Congolese soldiers as well as one civilian were killed in clashes overnight between the army and the ADF-NALU some 40 kilometers north of Beni.

The ADF-NALU rebel group, which was founded in Uganda in 1995 and later moved to the Congo, is believed to have roughly 400 members and has been accused of committing serious human rights violations, including recruiting child soldiers and rape. The ADF-NALU rebels killed more than 300 villagers last year and around Beni.

They are engaged in trafficking gold and wood to finance themselves, which could further destabilize the vast region rich in minerals, the United Nations said.