A redacted report from an oversight court says the agency regularly accessed a database meant for foreign investigations.

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.

The issue has aligned staunch liberal defenders of civil liberties with allies of former President Donald Trump, who have long accused the FBI of unfairly targeting the Republican leader and his supporters.

It could also further bolster criticism from congressional Republicans, who have created a committee in the US House of Representatives to investigate the “weaponisation” of government.

In repeated episodes, the FBI’s own standards were not followed, according to the document, disclosed on Friday and issued last year by the Foreign Intelligence Surveillance Court, which has legal oversight over US government spy powers.

The document said 300,000 abuses were recorded between 2020 and early 2021.

In one instance, the FBI queried the Section 702 repository using the name of someone who was believed to have been at the Capitol during the January 6 riot.

Officials obtained the information despite it not having any “analytical, investigative or evidentiary purpose”, the order said.

In another episode, an FBI analyst ran 13 queries of people suspected of being involved in the Capitol riot to determine if they had any foreign ties, but the Department of Justice later determined that the searches were not likely to find foreign intelligence information or evidence of a crime.

Other violations occurred when FBI officials in June 2020 ran searches related to more than 100 people arrested in connection with the civil unrest and racial justice protests unfolding in the wake of the police killing of George Floyd in Minneapolis, Minnesota.

The court document said the FBI had maintained that the queries were likely to return foreign intelligence, although the reasons given for that assessment are mostly redacted.

Another violation included a query of 19,000 donors to an unnamed congressional campaign. Officials said the case involved a candidate who ran unsuccessfully and is not a sitting member of Congress.

Speaking on condition of anonymity to reporters after the report’s release, senior FBI officials attributed the majority of the violations to confusion among the workforce and a lack of common understanding about the querying standards.

They also said the violations predominantly occurred before the agency had made several reforms, saying the number of queries about US citizens has dropped dramatically following a series of audits.

In the court document released on Friday, a judge noted that the number of people with access to the database may need to be severely curtailed if the misuse persists.