The FBI has quietly revised its privacy rules for searching data involving Americans' international communications that was collected by the National Security Agency, US officials have confirmed to the Guardian.

The classified revisions were accepted by the secret US court that governs surveillance, during its annual recertification of the agencies' broad surveillance powers. The new rules affect a set of powers colloquially known as Section 702, the portion of the law that authorizes the NSA's sweeping "Prism" program to collect internet data. Section 702 falls under the Foreign Intelligence Surveillance Act (Fisa), and is a provision set to expire later this year.

A government civil liberties watchdog, the Privacy and Civil Liberties Oversight Group (PCLOB), alluded to the change in its recent overview of ongoing surveillance practices.

The watchdog confirmed in a 2014 report that the FBI is allowed direct access to the NSA's massive collections of international emails, texts and phone calls – which often include Americans on one end of the conversation. The activists also expressed concern that the FBI's "minimization" rules, for removing or limiting sensitive data that could identify Americans, did not reflect the bureau's easy access to the NSA's collected international communications.

FBI officials can search through the data, using Americans' identifying information, for what PCLOB called "routine" queries unrelated to national security. The oversight group recommended more safeguards around "the FBI's use and dissemination of Section 702 data in connection with non-foreign intelligence criminal matters".

As of 2014, the FBI was not even required to make note of when it searched the metadata, which includes the "to" or "from" lines of an email. Nor does it record how many of its data searches involve Americans' identifying details – a practice that apparently continued through 2015, based on documents released last February. The PCLOB called such searches "substantial", since the FBI keeps NSA-collected data with the information it acquires through more traditional means, such as individualized warrants.