More resources are needed to investigate and prosecute individuals who stole billions in pandemic relief funds, the Justice Department said in a report on Tuesday.

Federal officials said they have made “significant progress” in going after fraud, but conceded that “substantial work remains in the face of numerous challenges.” Agencies responsible for pursuing pandemic fraudsters have been restrained by budget cuts, according to the report.

The federal government, which distributed trillions in relief funds after the onset of the pandemic, has charged more than 3,500 defendants for offenses related to pandemic fraud, according to the report. That’s up from about 3,100 defendants who had been charged as of August. More than $1.4 billion in fraudulently obtained funds have been seized or forfeited.

Most cases have involved the Paycheck Protection Program, the Economic Injury Disaster Loan program and expanded unemployment benefits.

While the amount of stolen funds is unknown, the Small Business Administration’s inspector general estimated that more than $200 billion — or at least 17 percent of the roughly $1.2 trillion in pandemic loans the agency awarded — was distributed to “potentially fraudulent actors.”

The Government Accountability Office said that as much as $135 billion of the roughly $900 billion in unemployment benefits distributed between April 2020 and May 2023 were likely illegally claimed.

While most pandemic relief programs have largely ended, Justice Department officials said that state work force agencies continue to provide additional data that could be analyzed for leads. Some stolen relief funds also “remain restrained in bank accounts and need to be forfeited,” according to the report.

“The Justice Department is committed to continuing our efforts to investigate and prosecute pandemic relief fraud,” Attorney General Merrick B. Garland said.

The report also warned that cases could become harder to prosecute given the statute of limitations, which ranges from five to 10 years. The department is calling on lawmakers to pass legislation that would apply the 10-year statute to all pandemic fraud-related offenses.

“The statute of limitations must be extended and the necessary funding and data analytic tools secured for our prosecutors to recover hundreds of millions of dollars more in fraud proceeds,” Deputy Attorney General Lisa Monaco said in a statement.

White House officials have urged lawmakers to provide additional funding to help law enforcement officials prosecute cases. On Tuesday, three Democratic senators introduced legislation that would, among other things, provide $300 million to help the Justice Department beef up enforcement.

President Biden “strongly supports” the legislation, which would enact many of the pandemic-fraud proposals the president released last year, White House officials said.

After the pandemic shut down much of the economy, the federal government distributed trillions in relief funds meant to help American households and small businesses recover. But in the federal government’s haste to get money out the door, much of it was distributed with few strings attached. As a result, billions of taxpayer funds were stolen by thousands of people, ranging from sophisticated criminals to amateur fraudsters.

Federal officials have been trying to catch up to the wave of fraud for years. In addition to U.S. attorney’s offices, hundreds of people across more than 40 offices of inspectors general are working on pandemic fraud investigations, as are agents from the F.B.I., the Secret Service, the Postal Inspection Service, Homeland Security Investigations and Internal Revenue Service Criminal Investigation.

Federal prosecutors have deployed various methods to try to catch wrongdoers. At the U.S. attorney’s office in Maryland, officials have started to screen people suspected of violent crime and illegal possession of firearms for pandemic fraud. Officials at the U.S. attorney’s office in the Northern District of Mississippi have also asked county officials to review lists of individuals who received pandemic loans.

But rooting out people who exploited pandemic-relief programs has been a challenging task, given the sheer volume of fraud. Officials have conceded that some smaller-dollar thefts may never be prosecuted.

Responding to the wave of pandemic fraud has also made federal officials “keenly aware of the need for a permanent, interagency body” to combat government benefits fraud, given that some fraudsters appear to be applying the criminal skills and tools they acquired during the pandemic to continue to attack programs, according to the report.