The U.S. Secret Service says it has intercepted a threatening letter addressed to U.S. President Barack Obama that was similar to ones sent to New York Mayor Michael Bloomberg.
Letters sent to Bloomberg and his gun-control group contained material believed to be the deadly poison ricin and contained a reference to gun control.
A Secret Service official on May 30 said the White House letter was similar but did not elaborate.
Authorities have stopped several ricin-laced letters in recent weeks.
A man was charged last month with sending poison-laced letters to Obama and two other public officials.
Based on reporting by Reuters and AP