FBI Director Christopher Wray warned Congress on Wednesday that terrorist groups are looking to use drones to wage attacks in the U.S.

“I think we do know that terrorist organizations have an interest in using drones,” Wray testified in a hearing for the Senate Homeland Security and Government Affairs Committee.

“We’ve seen that overseas already with growing frequency. I think the expectation is that it’s coming here imminently. I think they are relatively easy to acquire, relatively easy to operate, and quite difficult to disrupt and monitor,” Wray added.

Nicholas Rasmussen, the director of the National Counterterrorism Center echoed Wray’s concerns.