The Federal Bureau of Investigation has 130 cases tied to cryptocurrencies, according to an agent speaking at a digital-asset industry conference in New York.

The cases “threat tagged” to virtual currencies encompass crimes such as human trafficking, illicit drug sales, kidnapping and ransomware attacks, according to Kyle Armstrong, a supervisory special agent.

“There are thousands of cases in the bureau, so it is a small sliver at this point,” Armstrong said at the Crypto Evolved conference Wednesday. The agency has noticed an increase in illegal activity facilitated by digital-currency payments, he added.

The opioid epidemic, in particular, has come into focus at the FBI as the “dark web” enables a surge in drug abuse. Illegal online marketplaces are where 10 percent of global drug users make their purchases, said Armstrong, who is in charge of the FBI’s virtual-currency initiative, which has been around for about three years.

The FBI has also seen a significant rise in extortion schemes related to virtual currencies on the southwest border of the U.S., Armstrong said.

While Armstrong said the agency takes a neutral view on digital tokens, he noted several pros and cons. The distributed ledger that underpins blockchain technology makes it easier to trace cryptocurrencies than cash, for example, but the anonymity of the transactions can be a hurdle to legal investigations, he said.