The FBI made material errors in at least two applications to the Foreign Intelligence Surveillance Court in 2019, according to a newly unsealed court filing that shows Justice Department internal reviews of such national security cases have been put on hold during the coronavirus pandemic.

In a 54-page submission to the court created by the Foreign Intelligence Surveillance Act, better known as the FISA court, the Justice Department explained in detail how it and the FBI are trying to correct problems in the FISA process that came to light as a result of the 2016 investigation of advisers to Donald Trump’s presidential campaign. The FISA court is used to pursue the most important national security cases involving terrorism or espionage.

Last year, Justice Department Inspector General Michael Horowitz found 17 serious errors or omissions in FISA applications for surveillance on Carter Page, a former Trump campaign adviser. As a result, Horowitz launched a broader audit of the FBI’s FISA work. In a memorandum filed last month, Horowitz said he had also found problems with every one of more than two dozen FISA applications sampled as a part of that audit, which is not yet complete.

President Trump has argued that the errors in the Page case showed the FBI launched a politically motivated witch hunt against him, although Horowitz’s subsequent findings suggest a wider, systemic accountability problem in how the FBI has used the secret surveillance program. FBI Director Christopher A. Wray has announced more than 40 corrective actions to overhaul its FISA process.

In Horowitz’s recent memorandum, he said it was too early to say whether the new errors he had found were material, a legal term used to describe facts so central to the matter that they could have affected the court’s finding of probable cause to surveil a FISA target.

In the new Justice Department filing submitted last week and released in redacted form this week, the agency said its 2019 accuracy reviews of FISA applications found material errors in two applications, both counterintelligence cases. One application contained two material errors, while the other omitted material facts, according to the filing, which said the department has not completed its assessment of accuracy reviews for the year.

“In both of these cases, the Government reported these errors and omissions to the Court and assessed that, notwithstanding these errors or omissions, probable cause existed to find that the targets were acting as an agent of a foreign power,” the filing said.

A year earlier, the Justice Department found 329 errors in a sampling of 40 FISA applications but determined none of them were material.

The filing also said the Justice Department suspended accuracy reviews in March because of the coronavirus and will resume them once the pandemic has passed.

John Demers, the head of the Justice Department’s national security division, said the filing shows the department “takes its oversight responsibilities seriously and reports all potentially material errors to the Court promptly.”

Demers said that the department will restart accuracy reviews of FISA applications — which involve travel and face-to-face meetings — “as soon as we can” and that the oversight work will boost staffing by 50 percent for more-rigorous examinations and unannounced reviews. Some of those reviews, Demers said, will probe more deeply into FISA files to “ensure the completeness of the representations made in the applications.”

In a statement, the FBI said that the bureau is confident the corrective actions laid out last year by Wray “will address the errors in earlier FISA applications” and that it will continue to update the court “to ensure that our corrective steps are implemented in a timely manner and that our FISA authorities are exercised responsibly.”

In an interview on Fox News that aired Thursday, Attorney General William P. Barr said he felt officials could install safeguards that would make it “very hard” for agents to circumvent the FISA rules, either intentionally or out of sloppiness. Without naming anyone, he lashed out at those found to have done wrong in applying for surveillance warrants.

“The people who abused FISA have a lot to answer for, because this was an important tool to protect the American people,” Barr said. “They abused it. They undercut public confidence in FISA but also the FBI as an institution, and we have to rebuild that.”

Matt Zapotosky contributed to this report.