Australia's top law-enforcement agency has defended its use of a controversial law that requires internet service providers to block websites government agencies deem illegal, without judicial oversight.

Speaking before a parliamentary inquiry, Australian Federal Police's officials explained why they needed section 313 of the Telecommunications Act, which requires telcos such as Telstra and Optus to assist government agencies to enforce criminal laws, protect public revenue and safeguard national security.

The AFP has defended its use of a controversial power that it uses to block websites. Credit:Andrew Quilty

The AFP, financial regulator ASIC and an unidentified national security agency have interpreted the law to mean they have the power to order telcos to block websites hosting illegal material.

But internet providers such as iiNet and industry bodies such as the Australian Mobile Telecommunications Association (AMTA) and the Communications Alliance have called for restrictions. They argue there is not enough oversight and that some providers had even received blocking requests from animal protection agency the RSPCA.