Update at 5:29 p.m. ET: The envelope that ignited at a District of Columbia mail facility was addressed to Janet Napolitano,

the secretary of homeland security, The Associated Press reports, citing an unnamed official.

Update at 4:26 p.m. ET: No injuries reported at the mail-sorting facility, which was evacuated.

CNN says, citing a law enforcement source, that an employee had tossed the envelope into a sorting bin and smelled smoke. The envelope was not opened and did not go off in an employee's hands.

Update at 4:08 p.m. ET: The envelope is similar to the two packages that ignited yesterday in Maryland, the FBI says.

The parcels sent to Gov. Martin O'Malley and the state transportation secretary each contained a small battery and an electric match concealed in a small white box, law enforcement officials say. Two mailroom workers had their fingers singed while opening the envelopes, which produced a small flame, smoke and a sulfur smell.

Original post: An envelope has ignited at a post office in northeastern Washington, D.C., police say.

It's not yet known whether it's related to two packages sent to Maryland's governor and the transportation secretary that ignited yesterday when they were opened. Both contained the same angry note protesting highway signs urging motorists to report suspicious activity, investigators said today, The Associated Press reports.

The message read: "Report suspicious activity! Total Bull----! You have created a self fulfilling prophecy."

(Posted by Michael Winter)