On the last Sunday in March before Ramadan, thousands of merchants and villagers filled the market of Moura, in central Mali, trading cattle in a vast pen and stocking up on spices and vegetables in the town’s sandy alleys.

Suddenly, five low-flying helicopters thrummed overhead, some firing weapons and drawing gunfire in return. Villagers ran for their lives. But there was nowhere to escape: The helicopters were dropping soldiers on the town’s outskirts to block all the exits.

The soldiers were in pursuit of Islamist militants who have been operating in the region for years. Many of the soldiers were Malians, but they were accompanied by white foreigners wearing military fatigues and speaking a language that was neither English nor French, locals said.