GRAFTON, N.D. —The Grafton Police Department is warning residents of a phone scam in which one or multiple callers claim to have kidnapped the victim's child or grandchild and demand a ransom for their return.

Three people have reported the calls in Grafton and one person has reported a call in rural Walsh County. Grafton Police Chief Anthony Dumas said the victim in the first incident, which occurred around 10 a.m. Wednesday, Jan. 29, flagged him down in person while still on the phone with the suspect.

Dumas described the caller as "aggressive and demanding."

"It was the demands, and 'we have your daughter, you will listen to us, if I think you're reporting this to police I'll kill her right now, you'll never find her,' that kind of stuff," Dumas said.

After the initial call, Dumas said the police department notified the school attended by the victim's child and worked to verify the child was not in any danger.

Another victim who received the call told police the callers were threatening to kill his granddaughter unless he met their demands.

"Well, he had no grandchildren," Dumas said. "So he immediately knew that it was false."

The Grafton Police Department has notified state and regional investigation agencies, including the North Dakota Attorney General's Office, which is standard practice when police become aware of local phone scams.

Through investigation, Dumas said they have determined that the callers are using computer-generated phone numbers from outside the United States. The number of callers varies -- Dumas said on one call, it was just one man calling, on another call it was two men, and on a third call it was multiple men and a woman.

Rather than requesting a specific dollar amount, the callers demand victims go to their bank to withdraw money and tell the callers how much they have in their account.

Dumas said that, though the department is investigating the calls, scams that originate from outside the U.S. are difficult to pursue.

"Sometimes it does (get solved), sometimes it doesn't," he said. "I would say the batting average is not high on solvability when it's out-of-country."

Dumas reminded residents that if they receive a suspicious call, they shouldn't panic. Instead, they should make a note of the calling phone number and get in touch with law enforcement immediately.

"I would emphasize remaining calm," Dumas said. "The guy that flagged me down, he was very worked up, and I mean, understandably so -- you think someone has kidnapped your child, you know what I mean? But remain calm and notify authorities in any way that you can."