Even before last week's Paris attacks, U.S. officials had opened up a new front in the war on ISIS: cutting off its cash flow, NBC News reported.
The self-proclaimed Islamic state has "revenue streams (that) are, to be sure, diverse and deep," David Cohen, a senior Treasury official, said during a Washington speech last year, making it "probably the best-funded terrorist organization we have confronted."
While funding for the jihadists' global terror operations and ongoing control of Iraqi and Syria territories come from a variety of sources, an accurate accounting is problematic.
Much of the cash raised by ISIS, though, doesn't flow through conventional financial channels.
The Islamic State raises millions of dollars a week from "taxation" and outright extortion of businesses and local government and civilian workers, according to Howard Shatz, a senior economist at the Rand Corp.
"ISIS raises much of its money just as a well-organized criminal gang would do; it smuggles, it extorts, it skims, it fences, it kidnaps and it shakes down," he wrote in a blog post.