Foreign fighters and Islamic rebels, some of whom are aligned with al-Qaida, claimed authority over northern Mali last year following political upheaval in the nation's capital, Bamako.
Military sources were cited by the BBC as saying on background that government forces fired "warning shots" on unknown Islamic fighters who were making their way south.
Malian Defense Minister Col. Yamoussa Camara told Radio France International that "jihadist elements" had deployed along a de facto north-south line.
The U.N. Security Council has approved an African force for deployment to Mali to help ensure territorial integrity in the country. Salamatu Suleiman, head of political affairs of the Economic Community of West African Affairs, said last month the regional bloc was losing patience with Malian developments.
Dialogue is the preferred course of action, though "some of the elements involved in the crisis are not amenable to dialogue," she said in a statement.
Some rebel movements have agreed to peace talks set for this week in Burkina Faso.