A U.S. professor and his wife, accused of spying for Cuba, have pleaded not guilty in federal court.

Carlos and Elsa Alvarez appeared in a Miami, Florida, courtroom Thursday to face charges they spent decades sending information to Cuba about Cuban exiles in the United States.

The couple's attorneys say they plan to appeal a federal magistrate's order that they be considered a flight risk and kept in detention until trial.  No trial date has been set.

The Alvarezes were charged January ninth with being agents of a foreign power without registering with the U.S. government.  Prosecutors say they sent information to Cuba using shortwave radio and encryption equipment.

Federal Bureau of Investigation officials say there is no evidence they gave Cuba any classified or military information.

Some information for this report provided by AP.