French forces in Mali say the situation in the former Islamist stronghold of Diabaly is unclear, two days after militants withdrew from the town.
Last week French forces carried out air strikes on Diabaly, which had fallen to the Islamists on 14 January.
Malian and French forces have been patrolling the outskirts of Diabaly, the town's mayor told the BBC.
There are 2,000 French troops in Mali, fighting the Islamists who now control the northern half of the country.
The BBC's Mark Doyle, in town of Niono, 50km (30 miles) to the south, says military patrols are being sent from there into Diabaly, believed to be the base for the largest concentration of Islamists in central Mali.
Officials say the Islamists left Diabaly on Friday. However, the Malian military suspects the fighters are hiding in a nearby forest, our correspondent says.
"The situation in the vicinity of Diabaly is confused for the moment," a French colonel who gave his name only as Frederic told our correspondent.
A senior Malian military figure cautioned that parts of Diabaly's population were sympathetic to the Islamists, and this made their task difficult.
Officials say Mali's army has also retaken the town of Konna, whose capture by rebels triggered the French intervention.
French troops will remain the region for as long as necessary "to defeat terrorism", President Francois Hollande has said.
However, French Foreign Minister Laurent Fabius said on Saturday that West African countries must "pick up the baton" in the offensive to drive out the Islamists.
Ivory Coast President Alassane Ouattara also called for more support for Mali, at a summit of West African leaders in Abidjan attended by Mr Fabius..
The French foreign minister has said both Russia and Canada had offered logistical support.
Islamist militants in Algeria who seized a gas facility in the Sahara desert, killing foreign hostages, claimed the attack was in retaliation for the French intervention in Mali, though many analysts doubt this.