Four more bomb threats forced evacuations at stores in northeast Ohio early Friday, adding to a series of similar threats across the U.S. this week, the FBI said.

The latest threats were phoned in to a Wal-Mart in Mentor and Giant Eagle grocery stores in Mentor, Mentor-on-the-Lake and Green, authorities said. The stores were temporarily evacuated, but each reopened within three hours after police searches turned up nothing.

"We believe these are all tied into the same individual or group of individuals that are doing this all over the United States," FBI special agent Scott Wilson said.

The FBI and police said Wednesday they were investigating bomb threats at more than 15 stores in at least 11 states. The majority of the calls involve an extortion attempt, and the threats appear to be coming from overseas, Wilson said.

On Thursday, federal authorities said they were close to identifying one or more suspects.

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

He said the investigation was focused overseas, but declined to elaborate or say whether an arrest was imminent.

Large grocery and discount stores as well as banks in roughly a dozen states have received calls from an unidentified man who is able to provide such specific details that employees believe he is inside or somehow watching them.

In reality, authorities say, he may be calling from thousands of miles away, possibly Portugal, where the caller has asked the money to be wired.

On Thursday evening, the FBI provided an updated list of stores and banks believed to be traceable to the same suspect or group of suspects. The bureau is also investigating whether other reported threats are connected.

The FBI list includes: a credit union in Albuquerque, New Mexico; a Safeway store in Sandy, Ore.; a grocery store in Buchanan, Mich.; Wal-Marts in Newport, R.I., and Rio Grande City, Texas; bank branches at Wal-Marts in Salem, Va., and Fairlawn, Va.; a Macey's grocery store in Orem, Utah; a Dillons grocery store in Hutchinson, Kan., a bank branch in Milford, Conn.; a Von's in Vista, Calif., near San Diego; a bank in Savannah, Mo.; a bank in Ithaca, N.Y.; and banks in Tampa and Wesley Chapel, Fla.

In the Hutchinson case, in addition to ordering workers to wire him money, the caller ordered customers and employees to take off their clothes and threatened to force them to cut off a manager's fingers.

Similar calls made to stores in Hutchinson Wednesday were copycat crimes, police said. They took five people into custody.

The FBI has not said how much money was wired to the caller. But police in Newport said workers at a Wal-Mart were so frightened by a bomb threat on Tuesday that they wired $10,000 to the caller.

Authorities in Buchanan, Mich., had earlier said workers at a Harding's Market sent $3,000 to an account in Portugal. But on Thursday, Police Chief William Marx said flustered store employees made a mistake and the money was sent to Paraguay rather than Portugal, as the caller had demanded.

"They got their p's messed up," Marx said.