PRESCOTT, Ariz. -- Federal authorities said they are working with European authorities to identify suspects making threatening phone calls to more than 26 grocery stores, banks and discount stores in at least 17 states, including a Safeway in Prescott, within the past week.

There were at least eight new cases Friday in Ohio.

VIEW: KPHO.Com Coverage Of Arizona Mine Accident

The callers have threatened to set off a bomb unless store employees wire money to an account abroad.

"We certainly have some good leads," FBI spokesman Rich Kolko said from Washington. "We're close to identifying somebody who may be responsible."

"Up to this point these are hoaxes," Kolko said. "I think folks are catching on and not sending the money."

In Arizona, a bomb threat led to the evacuation of a Prescott Safeway on Tuesday.

A caller with an accent demanded $2,850, according to police and city spokesman Kim Kapin.

"The maximum that Western Union can send through its service is $3,000," Kapin said. Wiring money also includes a $150 service charge, Kapin added. "This individual was obviously aware of that."

Initially, the caller led employees to believe he was observing them.

"After a while, it sounded like he was just taking a shot in the dark at what they might be doing, or what they looked like or how they were reacting to his call," Prescott police Lt. Ken Morley said.

Sherry Johnson, a spokeswoman for Englewood, Colo.-based Western Union, said the company was working with the FBI and U.S. Secret Service to trace the money sent through the service.

It was also telling its agents to be on the lookout for the extortion plot.

"This is an ongoing law enforcement investigation," Johnson said.

Caller Tells Hostages To Strip; Threatens Amputations

A telephone caller making a bomb threat to a Hutchinson, Kan., grocery store kept more than 100 people hostage, demanding they disrobe and that the store wire money to his bank account.

SURVEY: Should A Company Pay A Bomb Scare Bribe?

"At this point, there's enough similarities that we think it's potentially one person or one group," Kolko said.

Police in Kansas safely led the 46 employees and 64 customers, some of whom had taken off their clothes, out of a Dillons grocery store after about 90 minutes.

Employee Marilyn Case told The Hutchinson News that store manager Mike Piros argued with the caller, but they relented when he continued to make threats and instructed them to "do it now."

He then demanded that one of Piros' fingers be cut off for every hour his demands were not met, and another employee got a butcher knife on his orders, Case said. Jim Peterson, a customer, told the newspaper that people became distraught.

"People came undone and started saying, 'No, no,"' he said.

Piros was not harmed. Police there initially said they were investigating whether the caller had hacked into the surveillance system, but later backed away from that possibility.

Authorities said the caller appeared to have visual access to the store, although officials were investigating whether the caller was out of state and may have hacked into the store's security system.

"If they can access the Internet, they can get to anything," Hutchinson Police Chief Dick Heitschmidt said. "Anyone in the whole world could have access, if that's what really happened."

On Wednesday, two other stores in Hutchinson also received bomb threats, said police Lt. Steven Nelson.

A bomb threat at a supermarket in Millinocket, Maine, on Wednesday was tied to the scam. Authorities there said a caller threatened to detonate a bomb inside the store unless money was wired to a bank account. Click here to read about the incident.

An unidentified man called a Newport Wal-Mart on Tuesday morning, saying he had a bomb and would harm employees. He also demanded that workers transfer $10,000 to an account, said Newport Police Sgt. James Quinn. The store wired the money, Quinn said.

FBI Targeting Overseas Connection

The FBI was compiling reports from local police departments to probe for similarities between the cases, Kolko said.

"At this point, there's enough similarities that we think it's potentially one person or one group," he said.

Police in Virginia said a similar threat was made at a store there on Tuesday. In that case, no money was sent and no bomb was found.

In Newport, the caller placed three separate calls to the store, Quinn said. An employee reported the bomb threat to police at 6:52 a.m., minutes before the store's scheduled opening.

Roughly 25 employees who were inside at the time were evacuated as a police SWAT team spent hours sweeping the building and bomb-sniffing dogs searched around cars in the parking lot. Neither the suspect nor any explosive device was found in the store, and no one was injured.

Quinn said police have identified the account where the money was wired, but he would not say where it was held. He said the caller used a land line from out of state, but would not say from where. No arrests have been made.

A similar call was made to a bank inside a Wal-Mart store in western Virginia late Tuesday morning, police said. An employee at a bank branch inside a Wal-Mart store in Salem was told that a bomb would explode unless an undisclosed amount of money was sent via Western Union. The store was evacuated and later reopened after no bombs were found, police said.

Another bomb threat was called in a few minutes later to a bank inside a store in Virginia's Pulaski County. That store was also evacuated and no bombs were found.

No arrests have been made in either of the Virginia incidents.

The store in Newport does not have a bank branch inside, but offers a money transfer service similar to Western Union, police said.

FBI Issued Guidelines

The FBI also issued guidelines on www.fbi.gov to business owners and suggests that employees get detailed information, asking for specifics about the bomb, what it looks like and when it will explode.

The FBI doesn't offer advice on whether to comply with the caller's demands for money.

"We can't advise companies whether to wire it or not, but we hope they'll be real careful before they hit the send key," Kolko said.

SLIDESHOW: Don't Miss These Simply Awww-some Pics

SLIDESHOW: Celebrities Commit Fashion Faux Pas

SLIDESHOW: World's Most Powerful Women Named

SLIDESHOW: View The Best Celebrity Mug Shots

VIDEO: Coke Cams Catch Thieves Undercover

SLIDESHOW: Cute Pets Strut In Fashion Week Show

SLIDESHOW: Dallas Cowboys Cheerleaders Delight Fans

SLIDESHOW: View Before and After Hairstyle Photos

ELSEWHERE ON KPHO.COM: A 13-year-old girl who went missing while riding an all-terrain vehicle in northwestern Arizona was found dead in a mine shaft, while her 10-year-old companion was rescued and airlifted to the hospital with serious injuries early Sunday, authorities said. CLICK HERE for details.