A test on an envelope that arrived at the White House Mail Screening Facility on Monday indicates that it contains cyanide, according to the Secret Service. The agency did not announce to whom the letter was addressed. Further tests are being conducted to confirm the results.

Secret Service spokesman Robert Hoback says:

"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. The sample was transported to another facility to confirm the results."As this is an ongoing investigation, the Secret Service will have no additional comment."

News of the intercepted letter was first reported Tuesday by The Intercept, which reports that the return address matches that of a man the Secret Service believes is responsible for other alarming packages received in the past 20 years.

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