Scammers are conning families of unaccompanied migrant children held at U.S. military bases in Texas and Oklahoma, convincing the relatives to pay nonexistent fees to be reunited with their loved ones, officials said.

The FBI has not determined how many people have fallen for the scheme. Con artists are using private information about the children to contact their family members and are demanding the families pay bogus processing and travel expenses to reunite the children with their relatives, reports the Daily Mail.

“With each day that passes, we identify new victims who have paid money and have suffered losses,” said Michelle Lee, spokeswoman for the San Antonio FBI office on Friday.

The FBI has not said how the scammers may have obtained personal information about the children.  No arrests have been made.

The scammers have contacted families of children staying at shelters at Lackland Air Force Base in San Antonio, TX and Fort Sill in Lawton, OK. The requested payments range from $300 to $6,000. Relatives in 12 states have been contacted, including Alabama, Florida and Massachusetts.

The U.S. Department of Health and Human Services is the agency in charge of the welfare of the children. The shelters are run by Baptist Child and Family Services, a San Antonio-based nonprofit, on behalf of the DHHS.

As part of the process to reunite the children with family members in the U.S., case workers for the nonprofit contact relatives. At some point after the initial contact, scammers have been calling relatives, demanding money to complete the reunification process, said Lee.

There are currently 999 children at the Lackland temporary shelter, said Kenneth Wolfe, a DHHS spokesman.  Thus far, 3,376 children have gone through the Lackland shelter. Fort Sill currently has 706 children, with 1,155 having gone through the facility.

More than 57,000 minors have arrived in the U.S. since October, mostly from El Salvador, Honduras and Guatemala.

“The well-being and safety of these children is our top priority and we take any reports of fraud very seriously,” said Kenneth Wolfe, a Department of Health and Human Services spokesman, in an email. “No direct payment to shelters will ever be requested during the reunification process.”

Investigators hope other victims will contact authorities. Any tips can be made anonymously to any FBI office around the country or on the agency’s web site, said Lee.