MOPTI, Mali — Salif Haidara sat drinking tea on the side of the road with other weary bus passengers when a man with a turban and a long beard approached them: Did they want to become holy warriors?

The skinny teen had left his poor hometown in the desert with only the yellow tank top, pants and plastic flip-flops he was wearing. Now Salif was being told he could earn 15,000 francs ($30) a day for himself and 200,000 francs ($400) a month for his family — an enormous sum for a boy who had just turned 16.

The car was waiting to take the recruits to a two-week-long training camp in Mali's vast desert, where they would learn how to fire weapons. But the man named Omar made one thing clear.