HACIPASA, Turkey (AP) — Sevda, a 22-year-old waitress in a brown apron, recounts how she made a small fortune running smuggled diesel from a village on Turkey’s wild and dangerous border with Syria. But the days when she could earn 20 times her salary waiting tables came to an abrupt end several months ago when police arrested her and slapped her employers with a massive fine.

The smuggled fuel came from oil wells in Iraq or Syria controlled by militants, including the Islamic State group, and was sold to middlemen who smuggled it across the Turkish-Syrian border. Western intelligence officials have alleged that Turkey is turning a blind eye to a flourishing trade that strengthens the Islamic State group, and Secretary of State John Kerry has called on Turkey to do more to stem the trade. Analysts estimate that the Islamic State group gets up to $3 million a day in revenue from oil fields seized in Iraq and Syria.