ANCHORAGE, Alaska (Reuters) - A U.S. Army specialist who was serving as a military policeman has been arrested at an Alaska military base on suspicion of spying, an Army spokesman said on Tuesday.

Specialist William Colton Millay, 22, was taken into custody at Joint Base Elmendorf-Richardson on October 28 following a joint espionage investigation by the FBI and Army Counterintelligence special agents, Army spokesman Lt. Col. Bill Coppernoll said.

"We do expect to prefer charges sometime this week," Coppernoll told Reuters. He said the charges would be brought under the Uniform Code of Military Justice, and the FBI said the case would be tried in military courts.

Coppernoll did not say who Millay, of Owensboro, Kentucky, was suspected of spying for or what sensitive information he may have had access to. He said the investigation was ongoing.

FBI spokesman Special Agent Eric Gonzalez said the arrest was not related to the WikiLeaks case, in which U.S. Army Private Bradley Manning is charged with downloading more than 150,000 diplomatic cables and passing some of them to WikiLeaks while working as an intelligence analyst in Iraq.

"It's unrelated, forget WikiLeaks," Gonzalez told Reuters.

Millay is assigned to the 164th Military Police Company, 793rd Military Police Battalion, 2nd Engineer Brigade.

Coppernoll said the 164th Military Police Company, known as the "Arctic Enforcers," was deployed to Afghanistan earlier this year but that Millay did not go.

"He was part of the rear detachment," Coppernoll said. "I don't know why in his particular case he was part of that (rear deployment) but that's not unusual."

A spokesman for the Anchorage Correctional Complex said Millay was being held there on a federal charge.

"Today's arrest was the result of a close working relationship between the FBI and its military partners in Alaska," Mary Rook, special agent in charge of the FBI in Alaska, said in a statement.

"Through this ongoing partnership, we are better able to protect our nation," Rook said.

Joint Base Elmendorf-Richardson is a combined Army and U.S. Air Force facility near Anchorage.

(Reporting by Yereth Rosen, Writing by Dan Whitcomb; Editing by Greg McCune and Cynthia Johnston)

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