The Malian government in January asked for military support from former colonial power France to help fight al-Qaida and nomadic fighters that took control over northern parts of the African country in the wake of a 2012 coup.
French Col. Gilles Jaron was quoted by television channel France 24 as saying a large-scale offensive is under way in Mali to respond to renewed insurgent activity.
"We know that not all of these terrorist groups ... in Mali were eliminated," he said Thursday "And at times, they may resurface as we move toward legislative elections."
Legislative elections are scheduled next month. Presidential elections were held in August.
A statement issued Wednesday by the spokesman for U.N. Secretary-General Ban Ki-moon said "a number" of Chadian peacekeepers were killed in a suicide attack on a checkpoint in Tessalit, near the northern border with Algeria.
"This attack will not deter the determination of the United Nations to support the restoration of security, stability and sustainable peace in Mali," the statement read.