"At this point the package is in an isolated area of the building. We are going to treat it as if it is a hazardous substance until we know that it's not," said Minneapolis police spokesman Bill Palmer.
FBI spokesman E.K. Wilson said it's possible the package is one the hoax letters labeled "anthrax" that were sent to newspapers and TV stations around the country. The building was not evacuated.
A California man was arrested Wednesday on suspicion of sending more than 100 hoax letters labeled "anthrax" to newspapers and TV stations.
Marc M. Keyser, 66, sent more than 120 envelopes containing a compact disc that had a packet of sugar labeled "Anthrax Sample" along with a biohazard symbol, the FBI said in a news release.
None of the packets has so far tested positive for hazardous material, the agency said.
More mailings will probably be received over the next few days, authorities warned. Recipients should contact their FBI office, FBI agent Steve Dupre said Wednesday.
Dupre said the arrest is not connected to another series of bogus mailings containing a white powder that were sent to financial institutions and announced by the FBI last week.
Keyser was taken into custody without incident at his home in Sacramento on three counts of sending a hoax letter, the FBI said. At least some of the packages had Keyser's return address on them, said Dupre.
Keyser is being held at the Sacramento County jail and was expected to make his first court appearance Thursday. It wasn't known Wednesday evening whether he had a lawyer.
A message left for a Star Tribune spokesman was not returned Thursday. The newspaper reported on its Web site that its managers followed procedures for handling such cases, which have been in place since the Sept. 11 terrorist attacks.
"We don't think our employees have anything to worry about," said Star Tribune Executive Editor Nancy Barnes.
The investigation began after The Atlantic magazine received a letter Monday, Dupre said. The Charlotte Observer newspaper in North Carolina received an envelope Tuesday.
The Seattle Post-Intelligencer newsroom was evacuated briefly Wednesday after an editor opened a package that the FBI says appears to be connected to the other mailings. The Seattle Times reported it received a similar package.
The FBI collected the Post-Intelligencer's envelope. Seattle FBI spokeswoman Robbie Burroughs said it appeared to be part of a wave of mailings that originated in Sacramento, Calif.
"Out of an abundance of caution," she said the material would be sent to a lab for testing "but the assumption is that it is sugar."
The letters also were received Wednesday by at least one Sacramento television station, The San Diego Union-Tribune newspaper and the office of Republican Congressman George Radanovich in Modesto. A McDonald's restaurant in Sacramento also received a package.
Anthrax mailed to congressional offices and others in 2001 killed five people and sickened 17.
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