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Washington (CNN) -- An envelope that ignited Friday at a Washington postal sorting facility was addressed to Homeland Security Secretary Janet Napolitano, a department official confirmed.
Metropolitan Police Chief Cathy Lanier would not comment on markings on the package, or if it contained a note, but she said it was "similar in nature" to devices that ignited Thursday in two Maryland state offices.
Those devices carried messages apparently decrying road signs that ask motorists to report suspicious activity, a government official said.
At least one device was found, police said.
U.S. Postal Inspector Pete Rendina said inspectors were screening mail at facilities in the Washington metro area.
Napolitano, who was in Washington Friday, returned Thursday from a weeklong trip to Europe and the Middle East.
The building at 3300 V Street NE was evacuated, police spokeswoman Tisha Gant said. Law enforcement officers cleared the scene Friday evening without finding more devices.
The envelope that ignited was not opened and did not go off in an employee's hands, a law enforcement source said. The person tossed it into a sorting bin and then smelled smoke. A source on the scene said that all the employees had been accounted for.
Lanier said there were popping sounds, smoke and a brief flash of fire. No one was injured.
"It is an absolutely cowardly, reprehensible act," Washington Mayor Vincent Gray told reporters, echoing other officials who cited similarities in the Washington and Maryland incidents.
The facility -- which was built after the 2001 anthrax attacks to screen mail headed for federal offices -- is a few blocks from the District of Columbia's border with Maryland. Amtrak tracks are nearby.
Mailed devices containing a small battery and an electric match ignited in two Maryland state offices Thursday, mildly wounding two state employees when they opened the packages. The Maryland offices affected were in Baltimore and Annapolis.
Messages accompanying the devices used the words "report suspicious activity." Based on the packages' destinations, a government official told CNN he thinks the person was referring to flashing road signs posted on some Maryland roads that carry those words.
The message accompanying the device sent to the Maryland Department of Transportation headquarters read: "Report suspicious activity. Total Bulls--t. You have created a self-fulfilling prophecy."
According to the U.S. Bomb Data Center, between 2004 and 2008 there were 583 incendiary bombings resulting in 25 injuries and two deaths. Attempted incendiary bombings injured five and killed one person. The Bureau of Alcohol, Tobacco, Firearms and Explosives did not indicate how many were sent through the mail. The incidents this week were described as devices, not bombs.
CNN's Carol Cratty, Mike Ahlers, Jeanne Meserve and Eric Marrapodi contributed to this report.