The director of Russia’s federal security service, the FSB, has warned that terror groups are increasingly being financed through cryptocurrencies, Russian news site RBK reported on May 21.

FSB head Alexander Bortnikov said global terrorist organizations have been mastering the use of virtual currencies for some time, along with encrypted communication tools that enable them to evade security services. He added:

“Electronic payment systems and cryptocurrencies are increasingly being used by terrorists to move money received from some states and organizations that support the global terrorist network.”

According to Bortnikov, terror groups are also raising funds through the slave trade and by illegally selling oil.

In late April, the co-founder of Chainalysis warned that the crypto industry was beginning to see the beginnings of terrorism financing. Jonathan Levin added that bitcoin (BTC) was “by far the favorite” for hackers and criminals, as it was used in at least 95% of the incidents investigated by law enforcement.

Recent years have also seen crypto used to evade economic sanctions. In March, a U.N. Security Council report revealed that North Korea has managed to amass $670 million in fiat and cryptocurrencies through hacking attacks.