Lawmakers on Capitol Hill expressed concern Thursday over potential privacy and security threats from the use of domestic drones.

House members from both parties said steps need to be taken to protect privacy and prevent terrorists from taking over unmanned aircrafts before thousands begin to patrol American airspace.

Citing one incident last year, Texas Republican Rep. Michael McCaul warned terrorists are already planning how to manipulate the drones.

"The individual was arrested in September of 2011 after an undercover FBI investigation revealed his plot to use multiple remote-controlled aircraft laden with explosives to collapse the dome of the United States Capitol and attack the Pentagon," McCaul said.

The Department of Homeland Security declined to testify at the hearing and lawmakers say no federal agency is even willing to oversee domestic drones.

Witnesses also told lawmakers the signals used to guide civilian drones can be hacked, causing them to crash.

The Federal Aviation Administration said in the next five years some 10,000 drones will be used in the United States.