An envelope sent earlier this week to the White House has registered a “presumptive positive” test result for cyanide, a Secret Service spokesman said late Tuesday.

The letter was received Monday at a facility that screens mail for the White House and is located away from its grounds and the surrounding buildings in Washington.

The initial test on the envelope was negative, a second test Tuesday was “presumptive positive” and it has now been sent to another facility to confirm those results, according to spokesperson Robert Hoback.

Suspicious letters are often sent to some of the country’s leading politicians. Some test positive for hazardous materials, while other letters contain death threats or other physical harm.

In June 2013, a West Virginia man was indicted of charges of threatening to kill Obama and his family in a letter that included profanity and racial slurs. A federal judge later dismissed the charges after forensic handwriting analysis conducted by the Secret Service showed that 20-year-old Ryan Kirker, of McMechen, West Virginia, didn't write the letter.

Two months earlier, letters sent to Obama, Sen. Roger Wicker, R-Miss., and Mississippi judge Sadie Holland tested positive for the poison ricin. The letters addressed to the president and to the senator were intercepted before delivery, but one letter reached Holland. She was unharmed.

James Everett Dutschke of Tupelo, Mississippi, pleaded guilty in January 2014 to sending the letters and was sentenced to 25 years in prison.

The Intercept, which first broke the story, said the return address on the envelope that arrived Monday was that of a man who has sent multiple packages to the president’s home since 1995, including one package covered in urine and feces.

The Associated Press contributed to this report