Troops are in control of Kidal airport in northern Mali, seizing a key position in one of three provincial capitals the Islamist militants took last year.
French and Malian troops have recaptured two of the other cities, Timbuktu and Gao, in recent days.
Colonel Thierry Burkhard of the French army said the airport was taken overnight and described the operation in Kidal as “ongoing”.
Haminy Maiga, interim president of the Kidal regional assembly, said French forces met no resistance when they entered the town yesterday .
He said French troops and helicopters are in the city today.
The loss of Kidal would mean the Islamists no longer control any of the northern provincial capitals that they seized last April.
Mr Maiga said: "The French arrived at 9.30pm aboard four planes, which landed one after another. Afterwards they took the airport and then entered the town, and there was no combat. The French are patrolling the town and two helicopters are patrolling overhead.”
Yesterday, a secular Tuareg rebel group said they were in control of Kidal and other small towns in northern Mali.
Mr Maiga said those fighters had left Kidal and were at the entry posts on the roads from Gao and Tessalit.
France, the former colonial ruler, began sending in troops, helicopters and warplanes on January 11 to turn the tide after the armed Islamists began encroaching on the south, toward the capital.
French and Malian troops seized Gao at the weekend, welcomed by cheering crowds. They took Timbuktu on Monday.
The Islamists gave up both cities and retreated into the desert.
A US military official said the Pentagon is considering setting up a drone base in north west Africa to increase the collection of intelligence on the Islamists in their desert hideouts.