The seizure of Diabaly brings the Islamists to only 400 kilometers (250 miles) from the capital. Konna, the closest point where they were known to be before, is 680 kilometers (425 miles) away.
The ground assault reverses France's earlier insistence that it would provide only air and logistical support for a military intervention, which would be led by African troops. "Now we're on the ground," Guillaud said. "We will be in direct combat within hours."
On Tuesday, France announced it tripling the number of troops deployed to Mali from 800 to 2,500. The offensive was to have been led by thousands of African troops pledged by Mali's neighbors, but they have yet to arrive, leaving France alone to lead the operation.
Guillaud said the militant groups have a history of taking human shields and France would do its utmost to make sure civilians are not wrongly targeted. "When in doubt, we will not fire," he said.
A resident of Niono said that some residents of the besieged town had managed to slip through the rebel noose. They were arriving on foot, said Mamadou Haidara,
Hinnant reported from Paris. Associated Press writer Baba Ahmed in Bamako, Mali contributed to this report.