UNITED NATIONS, May 5 -- UN Secretary-General Ban Ki-moon on Tuesday strongly condemned the killing of two UN peacekeepers when a UN peacekeeping mission was ambushed in the eastern Democratic Republic of Congo (DRC).

According to a statement released by Ban's spokesperson, a convoy of the UN Mission for Stabilization of Congo (MONUSCO) was ambushed earlier Tuesday and came under fire from suspected Allied Democratic Forces (ADF) elements in Beni territory, North Kivu.

The attack, which killed two peacekeepers and injured 13 others, took place when MONUSCO was carrying out its protection of civilians mandate. Four other peacekeepers are reported missing, the statement said.

Ban also condemned "in the strongest terms" the continuing atrocities perpetrated by the ADF against defenseless civilians in the Beni area.

The UN remains committed to taking all necessary actions in line with the Security Council resolution to protect civilians and neutralize armed groups in the eastern DRC, the statement said.

The ADF formed in the mid-1990s in the Ruwenzori mountain range in western Uganda, and is believed to have killed more than 260 people in the final three months of last year in the eastern DRC, mostly using knives and machetes. In its most recent attack against civilians, the ADF reportedly killed 18 people in the Beni area last month.

The MONUSCO has been authorized to use all necessary means to carry out its mandate relating to the protection of civilians, humanitarian personnel and human rights defenders under imminent threat of physical violence.

Reports said a MONUSCO helicopter was hit on Monday by gunfire from unidentified armed elements in the same area.