“We are dedicating a lot of resources very specifically to this space,” Sigal Mandelker, the Treasury Department’s under secretary for terrorism and financial intelligence, said in an interview. “It is still relatively new to them, but I’m confident that we’re going to see more of it in the future.”

Cryptocurrencies are attractive to lawbreakers because they make it possible to hold and transfer money without a central authority, like PayPal, that can shut down accounts and freeze funds. Anyone in the world can create a Bitcoin address and begin receiving digital tokens without even providing a name or an address.

The online markets where Bitcoin can buy drugs are hosting nearly $1 billion in commerce a year, even as the authorities have shut down numerous leading markets.

Countries that are facing American economic sanctions, like Iran, Venezuela and Russia, have also taken steps toward creating their own cryptocurrencies to circumvent them.

Bitcoin has been slower to take off among terrorists in part because of its technical sophistication, terrorism experts said. Terrorist groups have also had methods of using the traditional financial system without needing Bitcoin.

Hamas, which controls the Palestinian coastal territory of Gaza, has traditionally survived on hundreds of millions of dollars of donations from foreign governments like Qatar. The Islamic State in Syria subsisted on taxes and fees it collected in the territories it controlled.

But both organizations have seen their access to money significantly curtailed. Israel maintains a strict blockade of Gaza, with Egypt’s help, and Hamas has been squeezed over the last year by financial cuts imposed by the rival, Western-backed Palestinian Authority. And the Islamic State has lost most of its territory.