But he told Congress in June that Islamic State had made nearly $1 billion during 2015 — mainly from illicit oil sales and extortion from businesses in territory held by the group.
Islamic State financing needs a crackdown, U.S. expert says →
"When we see indications that ISIL cannot pay the salaries of its own fighters … we know we are hitting them where it hurts," he said, adding that "we are also seeing internal corruption rising.
Bombings force ISIS to cut fighter pay by half: U.S. officials →
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