The FBI claims technology promoted by Apple and WhatsApp is helping ISIS

Encryption is creating "dark spaces" that are aiding ISIS and other terrorist organisations, the FBI has warned - even as Apple and Facebook reaffirm their strong support for the technology.

Speaking at a Congressional hearing on Wednesday, the AFP reports, FBI assistant director of counter-terrorism warned lawmakers that strong encryption technology allows terrorists "a free zone by which to recruit, radicalize, plot and plan."

Steinbach is calling for "legal remedies" that will allow law enforcement access to encrypted communications.

Strong encryption has become a contentious subject recently. The term refers to messages or data masked in such a way that it is impossible to understand unless you have the correct key to decrypt it - even if you have a warrant. Encryption can help protect people protect their communications online, but authorities fear that it puts the communications of criminals out of their reach.

Following Edward Snowden's revelations about mass surveillance by the NSA, tech companies have increasingly moved to incorporate strong encryption into their products. WhatsApp uses end-to-end encryption, for example, meaning it is impossible for the messaging service to know what is being sent on its platform.

Apple is a particularly outspoken defender of encryption technology. Last year, it introduced encryption on its mobile platform iOS by default, infuriating law enforcement. One senior US police officer warned that the iPhone would become "the phone of choice for the pedophile" as a result. But the Cupertino company has stuck to its guns, and this week CEO Tim Cook made an impassioned defence of encryption at an awards dinner.

Cook slammed attempts by law enforcement to have backdoors introduced as "incredibly dangerous," saying encryption is "a critical feature for our customers who want to keep their data secure... If you put a key under the mat for the cops, a burglar can find it, too. Criminals are using every technology tool at their disposal to hack into people's accounts. If they know there's a key hidden somewhere, they won't stop until they find it ... Removing encryption tools from our products altogether, as some in Washington would like us to do, would only hurt law-abiding citizens who rely on us to protect their data. The bad guys will still encrypt; it's easy to do and readily available."

Steinbach's comments also come after Facebook recently introduced support for encryption on its social network. Users can now list their "public key" on their profile that others can use to contact them securely, and Facebook will also send messages to users in an encrypted format if they opt in.

The senior FBI official didn't single out companies that use encryption by name, but said that "some of these [social media] companies build their business model around end-to-end encryption," the AP reports. As a result, "the companies have built a product that doesn't allow them to help."

In his prepared remarks, he warned that "changing forms of internet communication are quickly outpacing laws and technology designed to allow for the lawful intercept of communication content," and that terrorist groups like ISIS and their communications are "going dark" as a result.

Chairman of the Committee Michael McCaul says this is a "tremendous threat to our homeland."

However, this position has been criticised by another US congressman - Rep. Ted Lieu from California. With a background in computer science, Lieu has been an outspoken advocate of encryption technology, writing a 3-point letter this week outlining its alleged merits.

Lieu told The Intercept that "the notion that encryption is somehow different than other forms of destroying and hiding things is simply not true," Lieu told The Intercept. "Forty years ago, you could make the statement that paper shredders are one of the most damaging things to national security because they destroy documents that law enforcement might want to see."

Furthermore, "dark spaces" already exist, the politician argues, and we visit them every day. "you have a dark place in your home you can talk, you can meet in a park -- there are a zillion dark places the FBI will never get to and they shouldn't because we don't want to be monitored in our home."

FBI director James Comey has previously slammed companies like Apple for using the tech, contending that they are aiding "bad guys" by doing so. And while Obama hasn't called for an outright ban, he wants to be able to track communications when possible. "When we have the ability to track [online communication] in a way that is legal, conforms with due process, rule of law, and presents oversight, then that's a capability we have to preserve," he said in January.

UK Prime Minister David Cameron has also suggested he may outlaw the tech entirely - something critics have said is totally unfeasible.