File Photo: A UN peacekeeper patrols near the border crossing point between Rwanda and the Democratic Republic of Congo in Goma Aug. 29, 2013. (Xinhua/REUTERS)

UNITED NATIONS, Nov. 15 (Xinhua) -- UN Secretary-General Antonio Guterres condemned the killing of UN peacekeepers on operations in the eastern part of the Democratic Republic of Congo (DRC), his spokesperson said Thursday.

At least 20 soldiers were killed, including seven Malawian and one Tanzanian UN peacekeepers and 12 people from the DRC, according to latest report.

The peacekeepers were killed Wednesday during joint operations in North Kivu province near the Ugandan border with the Armed Forces of the DRC against the Allied Democratic Forces (ADF), a rebel group in both the DRC and Uganda.

"The secretary-general expresses his deepest sympathy and heartfelt condolences to the families of the killed peacekeepers and the governments and people of the Republic of Malawi and the United Republic of Tanzania," the spokesperson said in a statement.

Guterres conveyed his support to the Malawian and Tanzanian contingents, "which continue to operate in an exceptionally difficult environment to protect local populations against the attacks of the ADF and other armed groups," it added.

The UN chief called on all armed groups to stop their destabilizing activities, and encourages the DRC authorities to continue taking the necessary measures to apprehend and bring to justice the perpetrators of attacks against civilians, national security forces and peacekeepers, the statement said.

The east of the DRC has been plagued by insurgency for over 20 years. The past year has seen a surge in violence around North Kivu.