The Islamic fighters have stolen equipment from construction companies, including more than $11 million worth from a French company called SOGEA-SATOM, according to Elie Arama, who works with the European Development Fund. The company had been contracted to build a European Union-financed highway in the north between Timbuktu and the village of Goma Coura. An employee of SOGEA-SATOM in Bamako declined to comment.

The official from Kidal said his constituents have reported seeing Islamic fighters with construction equipment riding in convoys behind 4-by-4 trucks draped with their signature black flag. His contacts among the fighters, including friends from secondary school, have told him they have created two bases, around 200 to 300 kilometers (120 and 180 miles) north of Kidal, in the austere, rocky desert.

The first base is occupied by al-Qaida’s local fighters in the hills of Teghergharte, a region the official compared to Afghanistan’s Tora Bora.

‘‘The Islamists have dug tunnels, made roads, they've brought in generators, and solar panels in order to have electricity,’’ he said. ‘‘They live inside the rocks.’’

Still further north, near Boghassa, is the second base, created by fighters from Ansar Dine. They too have used seized explosives, bulldozers and sledgehammers to make passages in the hills, he said.

In addition to creating defenses, the fighters are amassing supplies, experts said. A local who was taken by Islamists into a cave in the region of Kidal described an enormous room, where several cars were parked. Along the walls, he counted up to 100 barrels of gasoline, according to the man’s testimony to New York-based Human Rights Watch.

In Timbuktu, the fighters are becoming more entrenched with each passing day, warned Mayor Ousmane Halle. Earlier in the year, he said, the Islamists left his city in a hurry after France called for an imminent military intervention. They returned when the U.N. released a report arguing for a more cautious approach.

‘‘At first you could see that they were anxious,’’ said Halle by telephone. ‘‘The more the date is pushed back, the more reinforcements they are able to get, the more prepared they become.’’

In the regional capital of Gao, a young man told The Associated Press that he and several others were offered 10,000 francs a day by al-Qaida’s local commanders (around $20), a rate several times the normal wage, to clear rocks and debris, and dig trenches. The youth said he saw Caterpillars and earth movers inside an Islamist camp at a former Malian military base 7 kilometers (4 miles) from Gao.

The fighters are piling mountains of sand from the ground along the dirt roads to force cars onto the pavement, where they have checkpoints everywhere, he said. In addition, they are modifying their all-terrain vehicles to mount them with arms.

‘‘On the backs of their cars, it looks like they are mounting pipes,’’ he said, describing a shape he thinks might be a rocket or missile launcher. ‘‘They are preparing themselves. Everyone is scared.’’

A university student from Gao confirmed seeing the modified cars. He said he also saw deep holes dug on the sides of the highway, possibly to give protection to fighters shooting at cars, along with cement barriers with small holes for guns.

In Gao, residents routinely see Moktar Belmoktar, the one-eyed emir of the al-Qaida-linked cell that grabbed Fowler in 2008. Belmoktar, a native Algerian, traveled to Afghanistan in the 1980s and trained in Osama bin Laden’s camp in Jalalabad, according to research by the Jamestown Foundation. His lieutenant Oumar Ould Hamaha, whom Fowler identified as one of his captors, brushed off questions about the tunnels and caves but said the fighters are prepared.

‘‘We consider this land our land. It’s an Islamic territory,’’ he said, reached by telephone in an undisclosed location. ‘‘Right now our field of operation is Mali. If they bomb us, we are going to hit back everywhere.’’

He added that the threat of military intervention has helped recruit new fighters, including from Western countries.