Authorities estimate that at least 30,000 calls from Jamaica are made every day trying to defraud U.S. citizens.

A federal indictment unsealed Wednesday in North Dakota charges 15 defendants with bilking people out of more than $1 million, one of numerous lottery scams originating in Jamaica that allegedly targeted elderly Americans.

Prosecutors say the list of at least 20 victims included an 83-year-old woman in North Dakota who sent seven separate checks for nearly $158,000, after she was promised a prize of $19 million in cash. A South Dakota man allegedly sent a $14,000 cashier's check after he was told he won $3.5 million and a 2012 Mercedes.

U.S. Attorney Timothy Purdon of North Dakota said he could not comment specifically on the charges because it's an open case. But he suggested that people discuss possible scams with elderly family members.

"If someone calls you and asks you for money to claim a lottery or sweepstakes prize, it's a scam," Purdon said.

The indictment listed the names of the 15 people charged but not where they live, although most are believed to be from Jamaica.

Jamaican lottery schemes have been happening for many years. The Jamaican and U.S. governments set up a task force in 2009 to stop the scams, but the problem has gotten worse. Authorities estimate that at least 30,000 calls from Jamaica are made every day trying to defraud U.S. citizens.

The government said in the 33-page indictment that at least 10 of the victims are over 55 years old. Besides the victims from the Dakotas, investigators have identified targets in New York, New Hampshire, South Carolina, California and Florida.

Court documents show that the North Dakota victim started receiving calls in September 2011 from a caller who claimed to be with American Cash Awards. She was told she could claim the $19 million if she paid the outstanding taxes. The woman sent checks to a post office box in Deerfield, Fla.

The woman told she couldn't tell anyone or she might lose out on the prize. At one point she obtained a loan on a life insurance policy to pony up more money, documents show.

The South Dakota man also was asked to pay taxes and fees to get his prize. He was told after sending the initial $14,000 that he needed to send $5,000 in cash to the North Dakota woman, after which he sent play money. The man received a call a few days later from someone who claimed to be with the FBI and said the victim could be arrested if he did not send real money.