Federal prosecutors have charged 61 entities in connection with a scam in which suspects posing as federal tax and immigration authorities allegedly bilked 15,000 people out of more than $300 million.

Officials with the U.S. Justice Department said Thursday that the defendants were involved with an Indian-based call center operation that managed five call center groups located primarily in the U.S. and India.

Assistant Attorney General Leslie Caldwell said the operation manipulated primarily senior citizens and minorities and laundered the money with the help of prepaid debit cards.

WATCH: Justice's Caldwell: Scam Targeted Seniors, Minorities

Callers would pretend to be Internal Revenue Service or federal immigration agents and would threaten arrest, deportation or other punishment unless money was paid to resolve the phony issues.

"For nearly four years, this criminal network used a variety of schemes to trick, frighten individuals over the phone by tapping into their worst fear — that they would be arrested, they would be deported, they would face other problems with the U.S. government or with state and local law enforcement authorities," Caldwell told reporters in Washington.

Caldwell said the "coordinated takedown of this organization" was the result of the first multijurisdictional enforcement operation against the Indian call center scam industry.

Homeland Security Investigations official Bruce Foucart said the callers relentlessly pursued their targets.

WATCH: Scammers 'Menacing,' Homeland Security's Foucart Says

"These scammers in this case and so many cases like this are convincing," he said. "They are menacing and they are ruthless in their pursuit of their victims. They convey authority and a sense of urgency that leaves their victims terrified."

Federal law enforcement authorities are still pursuing at least 24 suspects in the U.S. and 32 other suspects who are believed to be living abroad.