Raleigh, N.C. — The FBI has launched an investigation into a letter mailed to John Edwards' presidential campaign office in Chapel Hill last week, authorities said Tuesday.

An envelope containing a white powder was sent to the campaign office last Wednesday, prompting officials to call for all campaign workers to evacuate.

White powder in letters has been associated with anthrax after an attack in 2001 killed five people and sickened 17. The substance was mailed to lawmakers on Capitol Hill and members of the news media in New York and Florida just weeks after the Sept. 11, 2001, terrorist attacks.

Tests at the State Laboratory for Public Health determined that the white powder didn't pose a health threat, so the campaign office reopened the following day.

The FBI investigation will focus primarily on the alleged use of weapons of mass destruction and hoax towards the Edwards office. The powder and the letter and envelope will be forwarded to the FBI lab in Quantico, Va., for further forensic testing.

Anyone with information about the case is asked to call the North Carolina FBI at 704-377-9200 or their nearest law enforcement office.