French and Malian forces squaring off with Islamist militants seized a key city from them Friday, a high-ranking French source told CNN.

The city is Konna, in the central region of Mali, a sprawling, landlocked Saharan nation. That region is the latest front in the grinding fight between the West and al Qaeda-linked militants.

The development is an important advance a week after France launched an air and ground military offensive against a strong militant presence across northern Mali and other locations in the sprawling country.

Insurgents advancing south toward the capital, Bamako, took Konna on January 10. They started retreating a week ago after the French and Malian forces pushed back, with attacks from the air and other firepower.

The fighting in Mali has captured the world's attention.

It was one of the most successful democracies in Africa until last year, when a coup toppled the president and Islamists capitalized on the chaos by establishing themselves in the north.

There, they imposed a strict interpretation of Sharia law, banning music, smoking, drinking and watching sports on television. They also damaged historic tombs and shrines.

France, once the colonial power in Mali, unleashed an offensive against the militants last week, a mission that President Francois Hollande says is designed to "destroy" the terrorist groups that have taken root.

French envoy stresses urgency

France is sending troops to Mali from military facilities in Africa and from France. Paris is seeking help from its regional allies and the international community.

Such assistance has its perils. After Algeria permitted France to use its airspace to take on insurgents, militants angry about the move stormed a gas field in eastern Algeria and took hostages in what is now an ongoing hostage crisis.

French Ambassador to Mali Christian Rouyer reiterated the need for the French offensive.

"We had a friendly country that was on the verge of dying," he told CNN in an interview Friday.

"It was absolutely necessary to act with urgency. We did it, I believe, with full knowledge of the reasons. Faced with the seriousness of the situation, to my knowledge, there was no other solution."

French military power has been boosted, he said, "because we know we have an adversary who's determined, who's not afraid, knows the terrain well and who's well-equipped."

The offensive has made an impact, stopping the "terrorist advance" and saving other towns: Mopti and Sevare, for example, Rouyer said.

"The advance of terrorist forces -- either in the western or eastern sectors -- has stopped," he said, adding that this is helping to establish calm in Bamako.

"If Mopti and Sevare had fallen into terrorist hands," he said, "I believe that today, we would have chaos in Bamako and all Mali."

France seeks help

Leaders from several countries have offered troops or logistical support for the offensive.