US Secret Service agents keep watch from the roof of the White House in Washington, March 17 2015. [Photo/Agencies]

WASHINGTON - The White House received an envelope this week whose chemical testing was positive for the poisonous stuff cyanide, the US Secret Service confirmed Tuesday.

"On Monday 3/16/15, an envelope was received at the White House Mail Screening Facility. Initial Biological testing was negative; however, on 03/17/15, the chemical testing returned a presumptive positive for cyanide," said a Secret Service statement. "The sample was transported to another facility to confirm the results."

According to law enforcement officials, there were no injuries or exposure concerns for the staff at the mail sorting facility who opened the envelope containing suspicious milky substance.

The US TV networks ABC News reported that the sender was someone known to the Secret Service and charges were possible, depending on the final results of the test.