LOS ANGELES — Authorities think that scammers calling wealthy Southern Californians to demand thousands of dollars in exchange for the return of children who they falsely claim have been kidnapped have roots in Mexico, specifically in Mexican prisons.

Law enforcement sources familiar with the crime told NBC News that suspects are becoming more sophisticated as they evolve from using Spanish and targeting immigrants in the United States to using English and dialing up targets in gilded communities like California's Beverly Hills and Laguna Beach.

The bureau is investigating two recent cases of "virtual kidnapping" in Laguna Beach.

A person uses a landline telephone on April 13, 2015. John Stillwell / PA via AP file

"We do believe that phone calls are coming from out of the country, including Mexico, and that money transfers have been sent out of the country," said FBI spokeswoman Laura Eimiller.

Police in Laguna Beach said scammers struck in their city, where the median asking price for a home is $2.9 million, on March 7 and 8.

Calls were received by unconnected Laguna Beach parents within a 24-hour period, Sgt. Jim Cota of the Laguna Beach Police Department said. In both cases, the parents thought the callers were being truthful when they said that their children had been kidnapped and would be released only if a ransom was paid.

Police were able to stop one victim — authorities did not identify the parents —who was driving to a Costa Mesa retailer to wire money to Mexico, Cota said.

The move saved the parent $6,000.

Police think the most recent scammers were sending victims to the same place, a Costa Mesa storefront where remittances to Mexico can be made.

The other victim was out $5,000 after making a cash withdrawal from a bank and then making the half-hour drive to Costa Mesa, Cota said.

Kathie Gross told NBC News she received such a call an hour after dropping her daughter off at school recently. The voice on the other end sounded like her daughter, Gross said: "She said, 'Mom they took me in a van. I don't know where I am.' I was speechless."

Gross thinks that when she uttered the name of her daughter, the scammers took note and subsequently used it — one reason authorities warn not to engage with the suspects.

Gross said she soon found her daughter safe at school.

Authorities think that suspects use social media to gather information about potential targets.

Federal law enforcement sources say hundreds of virtual kidnapping are reported each year, with many if not most of the victims residing in Southern California. The crime is heavily underreported, however, they say.

In some cases, investigators believe, the callers are Mexican prisoners, some of whom may have spent in the United States. Laguna Beach police investigated a case last year in which the suspect, Cota said, sounded like a convict.

Pedestrians walk along Forest Avenue in Laguna Beach, CA on March 4, 2019. Paul Bersebach / Orange County Register/SCNG file

"One of our detectives in 2018 actually got on the phone with one of these guys and said he sounded like a hardened criminal," he said. "He had some choice words for us — in English."

In September a federal judge in Houston sentenced 35-year-old Yanette Rodriguez Acosta to more than seven years behind bars for her role in a virtual kidnapping scam.

Prosecutors said Acosta's victims were told their children would be assaulted, raped and murdered if they didn't stay on the line, drive to a bank and then head to a Western Union or MoneyGram location to wire money in exchange for their child's release.

Police urge people who receive a ransom call to contact police as soon as possible.

"Hang up a phone and drive to the police department and let them know what just occurred," Cota said.