WASHINGTON, United States — US justice officials warned Monday that there was an "explosion" of incidents in which children were extorted for money after being persuaded to provide explicit images of themselves.

The Federal Bureau of Investigation said US law enforcement received more than 7,000 reports in the past year on financial sextortion of young children and teens that led to 3,000 victims.

Most of the cases involved boys and led to more than a dozen suicides, the FBI said.

It said many of the schemes originated from outside the United States, mainly from Nigeria and Ivory Coast.

Many of the schemes begin in chat rooms and online gaming sites, and the people behind them approach the victims using fake female identities.

They convince the victims to send explicit photos of themselves, and then threaten to make the photos public unless the victims send them money, often through peer-to-peer payment schemes, according to the FBI.

The victims are most often between 14 and 17, it said, but it had interviewed victims as young as 10.

"The shame, fear, and confusion that victims feel when they are caught in this cycle often prevents them from asking for help or reporting the abuse," the FBI said.

The FBI encouraged parents and those responsible for children to educate them on the threat of such online schemes.

"The FBI has seen a horrific increase in reports of financial sextortion schemes targeting minor boys -- and the fact is that the many victims who are afraid to come forward are not even included in those numbers," said FBI Director Christopher Wray in a statement.

"Victims may feel like there is no way out," said Wray. "It is up to all of us to reassure them that they are not in trouble, there is hope, and they are not alone."