Letters containing a "suspicious substance" were mailed to political figures who have expressed support for gun control measures in Washington and New York in the last two days, according to U.S. Capitol officials.
The FBI intercepted a letter Thursday addressed to President Barack Obama. A similar letter was sent to New York Mayor Michael Bloomberg Wednesday, according to news reports.
Officials at the U.S. Capitol are warning lawmakers there to be on the lookout.
"Please be advised that multiple mailings containing threats and a suspicious substance have been received at locations in New York and Washington, D.C.," according to Terrance W. Gainer, Senate Sergeant at Arms. "The suspicious substance in these cases has been preliminarily identified as ricin. Thus far, no mailings are known to have been received at a congressional office; however, I do not have sufficient information to assume letters arent destined for a Member at a state office or even their home."
The letters, he wrote, are addressed to individuals who have publicly expressed support of gun control legislation, postmarked out of Shreveport, Louisiana, on May 20, 2013 and mention the constitutional right to bear arms.
They arrived comes six weeks after ricin-laced letters were sent to Obama and Sen. Roger Wicker, R-Miss.