Jackson County authorities are investigating two mailboxes damaged by explosives early Sunday - one at a high school principal's residence - amid a rash of similar incidents in La Crosse County.

No one was injured by the Jackson County explosions, which happened in mailboxes near Hwy. 54 and Red School Road in the town of Melrose, Wis., said Jackson County Sheriff Duane Waldera.

But Melrose-Mindoro High School Principal Del Deberg reported his mailbox worth $25 was destroyed, according to sheriff's reports.

"This is definitely a public safety matter," Waldera said.

It's too early in the investigation to call the devices "homemade bombs," since little was left after they exploded to determine what was used, said Shannon Geisler, sheriff's administrative assistant.

Three explosive devices were found in La Crosse County mailboxes Saturday and Monday.

The La Crosse and Jackson County sheriff's departments are investigating similarities between the incidents, said La Crosse County sheriff's Capt. Kurt Papenfuss.

An unexploded duct tape-wrapped device about the size of a hand grenade with a fuse on one end was found in a mailbox outside a residence on Hwy. OA in the town of Barre, Wis., about 11:30 a.m. Saturday, Papenfuss said.

A second bomb destroyed a mailbox and started the post on fire outside a home on Pleasant Valley Road in the town of Hamilton, Wis., about 12:45 a.m. Monday.

Remnants of a third device that authorities believe was lit but did not explode were found about 1 p.m. Monday by a mail carrier at a home on Drektrah Coulee Road, off of Hwy. OA, Papenfuss said.

No one was injured by any of the devices. The incidents appear related, Papenfuss said, and evidence from all three sites was sent to the Wisconsin Crime Lab.

Two 22-year-old men were arrested Tuesday in Chippewa Falls, Wis., for setting off an explosive device in a remote area just before noon Sunday.

Anyone with information about the La Crosse County incidents should call the sheriff's department at (608) 785-9629 or La Crosse Crime Stoppers at (608) 784-TIPS. Information about the Jackson County incidents can be reported to the sheriff's department at (715) 284-5357 or Crime Stoppers at (800) 228-3203.