WASHINGTON — A vial containing the deadly poison ricin was found inside an envelope at a South Carolina postal facility, federal officials said Wednesday.

The FBI was investigating, but terrorism was not suspected.

“Based on the evidence obtained so far, we do not believe this is linked to terrorism but is related to threats criminal in nature,” said Brian Roehrkasse, spokesman for the Homeland Security Department.

A letter inside the envelope referenced legislation in Congress involving truckers and included an extortion threat against the government, according to a federal law enforcement official who spoke on condition of anonymity.

The envelope carried the typewritten message “caution-Ricin-poison” on the outside, according to the Greenville County Sheriff’s office. It arrived at a Greenville postal facility between 2 and 3 a.m. Oct. 15.

A postal worker noticed the wording, and law enforcement officials were summoned. The letter was sent to the Centers for Disease Control and Prevention, which determined Tuesday that the vial contained ricin.

Officials would not say to whom the envelope was addressed or where it was postmarked. The federal law enforcement official did say the letter was not addressed to a government official.

Postal Service spokesman Gerry McKiernan said tests on the envelope and the outside of the vial showed that none of the toxin leaked.

William Brown, spokesman for the postal facility in Greenville, said three employees came in contact with the envelope.

“There was no substance on the outside of the envelope at all,” Brown said. “We do not feel that there is any risk to the employees.”

Still, as a precaution, workers have been moved to another Greenville facility while tests are conducted on the building where the envelope was received.

The worst bioterrorism attack in U.S. history was perpetrated through the mail two years ago.

Five people died and 17 were sickened by anthrax-infected letters sent to media companies and the Capitol Hill offices of Democratic Sens. Tom Daschle of South Dakota and Patrick Leahy of Vermont.

The FBI repeatedly has warned local police about the possibility that terrorists might use ricin in an attempt to poison people through ventilation systems, through drinking supplies or in food.

British police earlier this year arrested seven members of an Algerian extremist group on charges of plotting to use ricin to kill a small number of people and terrify the London population.

Instructions for making ricin also were found in an al Qaeda safe house in Kabul, Afghanistan, according to the FBI.

Ricin also has been used in crimes in the United States that have no connection to terrorism. Last summer, a Washington state man was convicted of making and possessing about 3 grams of ricin, enough to kill 900 people.