Besides a Hannaford supermarket in Millinocket, at least 26 stores, banks and groceries in 15 states have been targeted by an international extortion scam that telephones false bomb threats in exchange for money wired overseas, the FBI said Friday.

Eight new threats, including four made Friday to three grocery stores and a Wal-Mart in northeast Ohio, have been discovered. Some pre-date Aug. 23, which was initially believed to be the day the threats started, said Special Agent Jason Pack of the FBI’s Washington, D.C., headquarters.

The FBI is working with local police and legal attaches at U.S. embassies in Europe to uncover suspects, Pack said. No arrests have occurred, although FBI investigators are close to identifying at least one suspect.

“We believe we have a pretty decent handle on it,” Pack said Friday.

The most recent threats were phoned in around 6 a.m. to a Wal-Mart and Giant Eagle stores in Mentor and neighboring Mentor-on-the-Lake and in Green, south of Akron, Ohio, authorities said. The stores were evacuated, but they reopened within three hours after police found no explosives.

In all cases, the caller claims to have a bomb placed inside the store that he threatens to detonate unless money is wired. The stores all have wire services, such as Hannaford’s Western Union, or other money transmission capabilities, Pack said.

In at least one case, the destination for the wired money has been Portugal, and one threat has been answered with a $10,000 wire transfer. Otherwise, no one has been hurt and no bombs have been discovered.

Other than the presence of wire transfer outlets, no real commonality is immediately apparent in the incidents or their locations, which range from Phoenix, Detroit and Philadelphia to small towns like Millinocket, where 36 people were locked down in the Central Street supermarket for about three hours Wednesday.

At least 30 state and local police, Penobscot County sheriff’s deputies and Millinocket firefighters closed about three miles of Central Street, or Route 157, effectively shutting down the town’s main economic artery for about six hours.

The Associated Press contributed to this report.