OMAHA, Neb. -- Rural carriers planned to deliver mail as scheduled on Monday despite the discovery of 14 mailbox pipe bombs across the Midwest in recent days, authorities said Sunday.
But postal officials warned customers that the doors of roadside mailboxes must be taped or otherwise kept open. Affected are customers in Nebraska, Iowa and northwest Illinois.
"We are instructing our carriers not to deliver to any closed receptacles," Mike Matuzek, U.S. Postal Service district manager for Nebraska and southwest Iowa, said Sunday.
Locked mailboxes, like those at apartment complexes and neighborhood delivery units, will have normal delivery, he said.
Matuzek called it a temporary precaution while the investigation continues. "It is deplorable," he said. "It brings a lot of innocent people into the fray of this thing where they really don't belong."
No arrests had been made in the case Sunday, as officials renewed pleas that whoever planted the bombs contact them and make their grievances clear.
"I hope whoever is responsible would respond," said Thayer County Sheriff David Lee, whose department received a call on one bomb found in a rural mailbox near Davenport on Saturday.
"The public is invited to view the letter, which may be recognizable to someone," the FBI said in a news release.
Six people were injured by explosions in Illinois and Iowa on Friday. None of the six bombs found Saturday in rural areas of Nebraska went off. They were later detonated harmlessly by authorities.
An anti-government note found with the bombs warned of more "attention getters."