Callers posing as tax and immigration agents are threatening arrest, deportation or other punishment unless money is sent to help clear up what they say is a deportation warrant or to cover supposedly unpaid income taxes.

The government says it's a scam that's tricked at least 15,000 people into shelling out more than $300 million.

In a first-of-its-kind nationwide takedown, the Justice Department announced charges Thursday against 61 defendants in the United States and abroad in connection with call center operations based in India.

As agents fanned out across the country to make arrests, officials in Washington advised the public that the callers on the other end of the line are fraudsters and not representatives of the United States government.

"The US government does not operate in this manner," said Assistant Attorney General Leslie Caldwell, head of the Justice Department's criminal division. "We never call to demand that money be loaded immediately onto prepaid cards. US government agencies do not call to demand immediate payments to avoid deportation or to avoid arrest."

The indictment, issued by a federal grand jury last week in the southern district of Texas, charges the defendants — which include five call centers in India  — with crimes including wire fraud, money laundering and false impersonation of an officer of the United States.

Defendants were arrested in multiple US cities Thursday, and the Justice Department is seeking the extradition of defendants still in India, Caldwell said.

The indictment outlines a complex web of criminal actors, each with a different role in the conspiracy.

Callers working off scripts and posing as officials with the Internal Revenue Service and US Immigration and Customs Enforcement would tell unsuspecting victims that they had failed to pay taxes they owed or were at risk of deportation, and that a fast payment was needed to get out of trouble.

Data brokers arranged the purchase of names and personal information of potential targets. "Runners" in the US were responsible for getting scammed funds into bank accounts, a laundering process aided through wire transfers and prepaid debit cards. And payment processors based in India helped facilitate overseas payments.

The scam is part of a pervasive pattern: The office of the treasury inspector general for tax administration said Thursday that more than 1.8 million people have reported that they've received an impersonation call.

Though the calls might appear to be obviously bogus, officials say savvy and successful individuals have nonetheless been duped, with the callers using information about their victims they'd learned through open-source means to present a facade of authenticity.

"The scammers in this case and so many like this are convincing. They are menacing and they are ruthless in their pursuit of their victims," said Bruce Foucart of ICE's Homeland Security Investigations. "They convey authority and a sense of urgency that leaves their victims terrified."

Among the victims: an elderly San Diego woman who forked over more than $12,000 after she was threatened with arrest if she didn't pay a penalty for fictitious tax violations.

A California man also paid $136,000 to resolve alleged tax violations after being called repeatedly over 20 days. And when a Colorado man did not respond to repeated demands that he withdraw funds to pay supposed back taxes, scammers posing as him called 911 and said he was armed and looking to kill police officers, prompting law enforcement officers to surround his home.

In a separate but similar call center scam, authorities in India said earlier this month that they'd arrested 70 people and were questioning hundreds more.

The Justice Department said it's not clear the victims will get their money back, and it's certainly possible that the arrested defendants could be replaced.

But Caldwell said the department wanted to send a message that "we are watching and we're paying attention to this, and we're taking appropriate action."