At least two suspected pipe bombs were found in mailboxes in Nebraska on Saturday, one day after six people were injured by pipe bombs exploding in rural mailboxes in Illinois and Iowa, authorities said.

Nebraska State Patrol spokeswoman Terri Teuber said bomb experts were headed to four locations in south-central Nebraska. She said there were reports of at least two devices in mailboxes that appeared to be pipe bombs.

It wasn't immediately clear if the devices had exploded or if they were linked to the bombs found Friday.

Chris Peterson, a spokesman for Nebraska Gov. Mike Johanns, said bombs had been reported in Howard, Platte, Fillmore and Thayer counties. He said that to his knowledge, none of the devices had gone off.

The Nebraska State Patrol issued an alert for rural residents to use caution when opening their mailboxes.