The attack is the first time the UN peacekeeping mission in Mali, MINUSMA, has recorded fatalities in the centre of a country long beset by violence in its vast and desolate north.
"According to preliminary information, five peacekeepers were killed. Another was seriously hurt and is being evacuated," MINUSMA said in a statement.
The UN did not immediately confirm the nationality of the dead soldiers but a Bamako police source indicated a group of Togolese peacekeepers "came across a mine and a terrorist attack some 50 kilometres out of Mopti."
MINUSMA mission head Mahamat Saleh Annadif condemned the attack as an "odious" act of terror.
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"I most strongly condemn this abject crime which adds to other terrorist acts targeting our peacekeepers and which constitute crimes against humanity under international law," said Annadif.
Today's attack came just two days after authorities reported five Malian soldiers killed and four wounded Friday when their vehicles hit a mine in the north and then came under sustained fire.
The Mali mission is the most dangerous active deployment for UN peacekeepers and it has been hit by sharp internal tensions since its launch in July 2013.
With today's attack, at least 64 MINUSMA peacekeepers have been killed while on active service, while another four have died in friendly fire incidents, UN figures show.
The north has seen repeated violence since it fell under the control of Tuareg-led rebels who allied with jihadist groups linked to Al-Qaeda in 2012.
Rival armed factions and smuggling networks mean the region has struggled for stability since Mali gained independence from former colonial power France in 1960.