The Federal Bureau of Investigations regularly misused a spy database while investigating suspects in the January 6, 2021 storming of the United States Capitol, according to a heavily redacted document from an oversight court.

The court document released on Friday shows the FBI used a special intelligence database containing foreign intelligence thousands of times while investigating US citizens — confirming a long-held concern that critics have had of the programme, launched in the wake of the September 11, 2001, attacks.

The database has been maintained under Section 702 of the Foreign Intelligence Surveillance Act, which expires at the end of the year. The latest revelations could threaten its renewal by Congress.