The explosion occurred between the central Segou and Mopti regions.
"We have lost five men. Their vehicle set off a mine. They were all in the same vehicle," a Malian military official told AFP yesterday.
Another Malian military source confirmed the blast and blamed "terrorists" for the killings, without naming any group.
Explosive devices and ambushes have been frequently used against Malian and UN forces, which arrived in 2013 to fight Islamists.
Northern Mali fell to jihadist groups linked to Al-Qaeda from March 2012. These forces were driven out of key towns by a French-led military intervention the following year.