“Bombing will weaken them, and it will stop their advance,” said Djallil Lounnas, an expert on the region at the University of Montreal who has written widely on Al Qaeda in the Islamic Maghreb, one of the main extremist groups in northern Mali. “But as soon as the bombing stops, they’ll come back.”

Since the French started bombing, he said, “the situation has changed slightly, but not fundamentally.”

Other analysts said that while forcing the insurgents from the cities was achievable, eliminating them altogether would require considerable additional effort.

“You can’t launch a war of extermination against a very tenacious and mobile adversary,” said Col. Michel Goya of the French Military Academy’s Strategic Research Institute. “We are in a classic counterinsurrectionary situation. They are well armed, but the weapons are not sophisticated. A couple of thousand men, very mobile.”

And they have been preparing for battle for months.

One resident of Gao who accompanied Islamist fighters to a desert hide-out in recent months described a vast system of underground caves big enough to drive cars into, said Corinne Dufka, a senior researcher at Human Rights Watch.

Around 100 Islamist fighters, many of them bearded foreigners speaking Arabic, had gathered inside, stockpiling weapons, vehicles, generators and scores of barrels of gasoline, the resident said. The bunker was well camouflaged, almost invisible from the rugged roads, and had long been used by bandits in the area. But the Islamists were expanding the tunnels and, even before the French campaign, had been gathering in them from towns across the north.

While striking the Islamists from the air, France was steadily building up its forces on the ground: 200 more soldiers and 60 armored vehicles arrived in Mali overnight on Tuesday from Ivory Coast, bringing the total to nearly 800 soldiers. The French Defense Ministry said the force would soon number 2,500, in the vicinity of its peak Afghanistan deployment. Late Tuesday, a French convoy was heading north from Bamako; a military spokesman refused to disclose its destination.