Ten United Nations peacekeepers were killed in a suspected al-Qaeda-linked terrorist attack upon a UN mission in Mali.
At least 25 others were also injured in the attack, the UN said in a media release, adding that the peacekeepers were Chadian nationals.
On Sunday, an unknown number of terrorists attacked a base belonging to the United Nations Multidimensional Integrated Stabilization Mission in Mali, or MINUSMA, located in Aguelhok in the northern part of the West African country, the peacekeeping mission said.
UN Secretary-General Antonio Guterres condemned the "complex attack" against MINUSMA in a statement issued by a spokesperson.
Guterres also said the attack against the UN peacekeepers may be considered a war crime, a statement reiterated by members of the UN Security Council in a media release of their own that condemned the attack "in the strangest terms."
Special Representative of the Secretary-General in Mali Mahamat Saleh Annadif said: "This complex and cowardly attack illustrates the terrorists' determination to sow chaos; it demands a robust, immediate and concerted response from all forces to wipe out the danger of terrorism in the Sahel."
"In close cooperation with its partners, MINUSMA will remain proactive and will not let this barbarity go unpunished," he said.
Guterres said he wishes for the "swift recovery to the injured" and he pays tribute to "the dedication and courage of the men and women serving in MINUSMA."
Al-Qaeda in the Islamic Maghreb, the northern African branch of Al-Qaeda, claimed responsibility, BBC News reported.
MINUSMA is one of the most dangerous peace operations in the UN's history, with 155 peacekeepers killed in Mali since it was established there in April 2013, the UN mission said.