Hazmat teams were called Thursday to the Philadelphia office of U.S. Sen. Pat Toomey.
Their response was prompted by a white powder found in a letter opened shortly before 3 p.m. by someone in Toomey's office, which is located in the 1600 block of JFK Boulevard, said Ofc. Tanya Little, a spokeswoman for the Philadelphia Police Dept.
No one was was hurt, and the office was not evacuated, although officials don't yet know what the powdery substance is. They also haven't said if the letter contained a message, who might have sent it or from where it was mailed.
The discovery comes a day after a message was sent to the U.S. Senate community that warned of a possible mail threat.
Letters containing a powdery substance were sent to at least three congressional offices this week, and the sender is threatening more that could include harmful material, said Sergeant at Arms Terrance Gainer, the top Senate law enforcement official.
"The author of these letters has indicated that additional letters containing a powdery substance will be arriving at more Senate offices and that some of these letters may contain an actual harmful material," Gainer's message said.
While the three letters received so far were harmless, "it is essential that we treat every piece of suspicious mail as if it may, in fact, be harmful," Gainer continued in his message.
Any letters postmarked from Portland, Ore., required special attention, especially those with a particular Portland return address, Gainer's message said. The Portland return address cited by Gainer did not appear to exist.
"If any mail is received from this return address, it should remain unopened and the local authorities contacted immediately, followed by notification to the United States Capitol Police Threat Assessment Section," Gainer's message said.
Federal and local law enforcement authorities are investigating the possible threat, according to Gainer.