INDIANOLA (AP) - Officials were investigating a suspicious powder found at the post office Monday morning.

The substance was on the outside of a letter, said Brian O'Keefe, spokesman for the Des Moines Fire Department, which sent a hazard materials crew to the scene. Indianola is just south of Des Moines.

"There's two people that are currently isolated," O'Keefe said.

O'Keefe said they were processing the mail when they discovered the substance on the letter.

He did not immediately know if the post office was closed. A telephone message left at the the Indianola police department Monday morning was not immediately returned.

On Friday, part of The Des Moines Register was evacuated and a street in front of the building in downtown Des Moines was closed after a suspicious powder was found in an envelope. The envelope, which contained a letter to the media, contained snail poison.

Des Moines firefighters responded to two other calls about suspicious substances over the weekend. The substances were harmless.