(CNN) -- Investigators suspect arson in a fire that heavily damaged a small post office in rural western Nevada Sunday morning, a U.S. Postal Service spokesman said.
Investigators found anti-government graffiti on the walls and bullet holes in the building, Capt. Mark Reagan of the Sierra Fire Protection District said.
"It's pretty bad," said David Rupert, describing the damage to the Verdi, Nevada, post office, which is located about 10 miles from Reno.
The fire began outside of the building, which houses postal boxes for about 800 residents, but water sprayed by firefighters soaked the mail inside, Rupert said.
The wet but unburned mail was taken to a postal facility in Reno to be resorted and delivered to customers, he said.
Agents from the Bureau of Alcohol, Tobacco, Firearms and Explosives and investigators from the U.S. Postal Inspector's office are conducting the probe, he said.
A sheriff's deputy responding to a burglar alarm that sounded at about 4:30 a.m. discovered the fire, Reagan said.
CNN's Greg Morrison contributed to this report.