CHICAGO, May 4: Five people were injured on Friday when seven pipe bombs exploded in mailboxes in rural Illinois and Iowa in what the FBI called an act of domestic terrorism.

Postal Service officials said the bombs — accompanied by anti-government messages — hurt four postal workers and a mailbox owner, but none of the injuries was life-threatening. One person suffered an eye injury and another received thumb and shoulder wounds.

Two other pipe bombs, found in Iowa mailboxes, failed to detonate and were being rendered safe, authorities said.

The Postal Inspection Service, which is coordinating the investigation, said the bombs were made of steel pipes, each with a 9-volt battery attached.

All the bombs appeared to have been planted in the mailboxes and did not arrive through the mail, the officials said.

“It appears the explosive devices were intended to detonate when they were removed from the mailboxes,” Postal Service representative Linda Jensen told a news conference in Des Moines.

The FBI, on heightened alert after the Sept. 11 attacks and deadly doses of anthrax sent through the mail last fall, described the mailbox bombings as “domestic terrorism.”

“We looked at the letters that accompanied these devices and are viewing it as a domestic terrorism incident,” FBI special agent James Bogner said.

He said the letters contained “general anti-government rhetoric.”

“My understanding is that they are all the same, similar letters, similar information,” Bogner said. The letters warned of future “attention-getters,” and were signed “someone who cares.”

Jensen said people should be very cautious when opening their mailboxes. “(The bombs) are accompanied by a clear plastic bag that contains a typewritten letter full of anti-government propaganda,” she said. “If such material is discovered by a postal customer or a postal carrier, please, please do not touch the item or slam the box door.”

Acting Chief Postal Inspector Jim Rowan said people should stop and look before removing mail from their mailboxes. “If you see a pipe in your mailbox, do not touch it or move it at all,” Rowan said in a statement.

“The bombs explode when they are moved,” he added, telling people to call police or the postal service if they found one.

Bogner said there could be other devices yet to be discovered. Mail carriers in the area were recalled from their routes.—Reuters