According to the New York Times, in Afghanistan, the Taliban have imposed an elaborate system to tax the cultivation, processing and shipment of opium, as well as other crops like wheat grown in the territory they control.
In the Middle East, Taliban leaders have sent fund-raisers to Arab countries to keep the insurgency's coffers brimming with cash.
Proceeds from the illicit drug trade alone range from 70 million dollars to 400 million dollars a year, according to Pentagon and United Nations officials.
By diversifying their revenue stream beyond opium, the Taliban are frustrating American and NATO efforts to weaken the insurgency by cutting off its economic lifelines, the officials say.
Despite efforts by the United States and its allies in the last year to cripple the Taliban's financing, using the military and intelligence, American officials acknowledge they barely made a dent.
"I don't believe we can significantly alter their effectiveness by cutting off their money right now," the paper quoted Representative Adam Smith, a Washington State Democrat on the House Intelligence and Armed Services Committees who traveled to Afghanistan and Pakistan last month, as saying.
"I'm not saying we shouldn't try. It's just bigger and more complex than we can effectively stop," he added.
American officials are debating whether cracking down on the drug trade will anger farmers dependent on it for their livelihood.