BAMAKO, Mali — Oumar Ould Hamaha, a notorious Islamist commander in the deserts of western Africa, has nothing but disdain for the international powers he opposes or the hapless Westerners he and other militants subject to extreme deprivation, hunger, thirst and proselytizing for months on end.

But he openly appreciates them for helping Islamists acquire the one thing they cannot do without.

“Lots of Western countries are paying enormous sums to the jihadists,” he said in a telephone interview from northern Mali, crowing about the hefty ransoms militants have collected in the region. “The source of our financing is the Western countries. They are paying for jihad.”

Kidnapping is such a lucrative industry for extremists in western Africa, netting them tens of millions of dollars in recent years, that it has reinforced their control over northern Mali and greatly complicated plans for an African-led military campaign to take back Islamist-held territory.

Beyond the immediate risk to the 10 Europeans and 3 Algerians still being held — “At the first strike, the hostages will have their throats cut like chickens, one after the other,” Mr. Hamaha threatened — an intervention could face formidable opponents. Al Qaeda in the Islamic Maghreb, one of the factions that have seized northern Mali, is estimated to have amassed as much as $90 million or more in ransoms over the past decade, turning it into one of the region’s wealthiest, best-armed militant groups.