Fresh clashes erupted overnight between the Malian army, backed by French troops, and Islamist insurgents encircling the central town of Konna, military sources said.
Fighting broke out on Wednesday near the town, whose capture by Islamist rebels last week prompted France to intervene in a bid to drive back the insurgents who have controlled northern Mali since April.
An Islamist militant said that the battle for control of the Konna area was "not finished".
The rebels pushed south into government-held territory last week and seized Konna, about 700 kilometres by road from the capital Bamako, prompting France to intervene.
While the Malian army earlier reported it had regained control of Konna, Jean-Yves Le Drian, the French defence minister, said the zone was still in the Islamists' hands. The area was not accessible to independent observers.
A Malian security source said that the town of Diabaly, where fighting raged between French troops and Islamists on Wednesday, remained under control of the extremists.
Insurgents seized the town, which lies 400 kilometres north of the capital, on Monday.