WASHINGTON (AP) — Fake US tax agents have targeted more than 366,000 Americans with harassing phone calls demanding payments and threatening jail as part of a huge nationwide tax scam that has cost taxpayers $15.5 million and partly involved call centers in India.

More than 3,000 people have fallen for the ruse since 2013, Timothy Camus, a Treasury deputy inspector general for tax administration, said Thursday.

The scam has claimed victims in almost every state, Camus said. One unidentified victim lost more than $500,000.

"The criminals do not discriminate. They are calling people everywhere, of all income levels and backgrounds," Camus told the Senate Finance Committee at a hearing. "The number of complaints we have received about this scam make it the largest, most pervasive impersonation scam in the history of our agency."

The scam is so widespread that investigators believe there is more than one group of perpetrators, including some overseas.

So far, Camus said, two people in Florida have been arrested. They were accused of being part of a scam that involved people in call centers in India contacting U.S. taxpayers and pretending to be agents of the tax agency.

"These criminal acts are perpetrated by thieves hiding behind telephone lines and computers, preying on honest taxpayers and robbing the Treasury of tens of billions of dollars every year," said Sen. Orrin Hatch, the Republican chairman of the Senate Finance Committee. "Taxpayers must be more aware of the risks and better protected from attack and these criminals must be found and brought to justice."

The inspector general's office started warning taxpayers about the scam a year ago, but it has since ballooned. Tax scams often increase during filing season, which ends April 15.

As part of the scam, fake tax agents call taxpayers, claim they owe taxes, and demand payment using a prepaid debit card or a wire transfer. Those who refuse are threatened with arrest, deportation or loss of a business or driver's license, Camus said.

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