The US Justice Department charged 61 people and entities on Thursday with taking part in a scam involving India-based call centers where sales agents impersonated US officials and demanded payments for nonexistent debts.
The scam, which had operated since 2013, targeted at least 15,000 people who lost more than $300 million.
Twenty people were arrested in the United States on Thursday, while 32 individuals and five call centers in India have been charged, the department said in a statement.
The defendants, including 24 people across nine US states, were indicted by a grand jury in the US District Court for the Southern District of Texas.
US Assistant Attorney General Leslie Caldwell said at a news conference that the United States will be seeking the extradition of those based in India and warned others engaged in similar schemes.
"It's really important for the scammers in India to know that the United States is looking at this, is watching them and they could, if they engage in that activity, be extradited to the United Sates and could sit in jail ... for several years," she said.
— Justice Department (@TheJusticeDept) October 27, 2016
According to the indictment, the operators of the call centers in Ahmedabad, in the Indian state of Gujarat, had sales agent impersonate US Internal Revenue Service, immigration and other federal officials and "threatened potential victims with arrest, imprisonment, fines or deportation if they did not pay taxes or penalties to the government."
Payments by victims were laundered by a US network of co-conspirators using prepaid debit cards or wire transfers, often using stolen or fake identities, the statement said.
The call centers also ran scams in which victims were offered short-term loans or grants on condition of providing good-faith deposits or payment of a processing fee, it said.
The investigation involved Immigration and Customs Enforcement, Treasury, Homeland Security, US Secret Service and police officials, the Justice Department said.
Earlier this month Indian police had detained a total of 772 employees in raids on nine call centres in a Mumbai suburb.
An Indian police official said several of the call center workers were high school graduates who were "very convincing in recorded conversations."
Callers were trained to switch their Indian accent for a passable American one. They studied a script six pages long that explained how conversations would develop, with tips on tackling doubts and suspicions.
They were paid between 10,000 rupees ($150) and 70,000 rupees ($1,050) every month, police said.