Intelligence agencies in the United States and United Kingdom can gain total control over anyone's smartphone by sending it a single text message, according to NSA whistleblower Edward Snowden.

Snowden told BBC in a new interview that the NSA has provided British security agency GCHQ with a sophisticated tool dubbed "Smurf Suite," which allows the agency to take over a smartphone by sending it an encrypted text message. And there is "very little" that a user can do to stop the agency from hijacking the device, he said, noting that the program itself cost $1 billion in the U.S.

"[They send] a specially crafted message that's texted to your number like any other text message, but when it arrives at your phone, it's hidden from you. It doesn't display. You paid for it, but whoever controls the software owns the phone. They want to own your phone instead of you," Snowden told BBC's investigative show Panorama.

Agencies can then access practically any function of the phone, allowing them to read text messages, call logs, browse web history, contact lists, geo-locations, wireless networks, and even take covert photos without the owner of the phone ever knowing.

Snowden went on to explain the various tools in the suite: "Dreamy Smurf is the power management tool which means turning your phone on and off with you knowing. Nosey Smurf is the 'hot mic' tool. For example if it's in your pocket, [GCHQ] can turn the microphone on and listen to everything that's going on around you - even if your phone is switched off because they've got the other tools for turning it on. Tracker Smurf is a geo-location tool which allows [GCHQ] to follow you with a greater precision than you would get from the typical triangulation of cellphone towers."

And then there is Paranoid Smurf, "a self-protection tool that's used hide the manipulation of your phone."

"For example," Snowden said, "if you wanted to take the phone in to get it serviced because you saw something strange going on or you suspected something was wrong, it makes it much more difficult for any technician to realize that anything's gone amiss."

Snowden described GCHQ as, for all intents and purposes, "a subsidiary of the NSA."

"They [the NSA] provide technology, they provide tasking and direction as to what they [GCHQ] should go after," he said.

GCHQ refused to directly address the allegations, citing a "long-standing policy that we do not comment on intelligence matters," according to BBC. "All of GCHQ's work is carried out in accordance with a strict legal and policy framework, which ensures that our activities are authorized, necessary and proportionate, and that there is rigorous oversight, including from the secretary of state, the interception and intelligence services commissioners and the Parliamentary Intelligence and Security Committee. All our operational processes rigorously support this position."

Snowden has been living in exile in Russia since 2013, when he provided journalists with classified information about the NSA's controversial surveillance programs. He recently said that he has "volunteered to go to prison with the government many times," but he has not received a response, as HNGN reported.