Moussa Ag Attaher of the Coordination of Azawad Movements said that they attacked the town of Tenenkou in the central Mopti region yesterday.
He said the violence was a reaction to the attack against the town of Menaka last week by groups allied with the government, which broke a cease-fire agreement.
"The attack in Tenenkou is a consequence of the violation of the cease-fire in Menaka," he said. "We want to show the Malian parties that we can also launch hostilities and we will mark our presence on all territories where we can."
Armed groups allied with the government attacked the northern town of Menaka last week, starting a surge of attacks by the coalition of separatists groups, also known by the acronym CMA.
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The violence threatens a peace accord meant to be signed May 15 between various armed groups, separatists and the government.
Radhia Achouri, a spokeswoman for the UN mission in Mali, confirmed the attack.
"We emphasise the cease-fire and respect of the cease-fire. We are very committed to the signature of a peace accord on May 15 and we invite all parties to move toward that," Achouri said.
Tuareg rebel groups seized control of northern Mali in early 2012 but then al-Qaida-linked Islamic extremist militants won control shortly afterward. Troops from former coloniser France later led a military offencive to dislodge the extremists.