MINNEAPOLIS (WCCO) – The FBI says a suspicious letter sent to a building near the Minneapolis-St. Paul International Airport has tested negative for concerning chemicals.

Four people sought medical assistance as a precaution after coming into contact with the letter, which was sent to the airport’s Federal Aviation Administration building. The building’s employees oversee aircraft certification, security, regulatory compliance and other airport functions.

The suspicious letter was taken to the Minnesota Department of Health’s Public Health Laboratory for testing. Officials say initial results came back negative for “biological agents of concern.”

FBI officials say they’re continuing to investigate the incident, and they have no comment on the status of who might have sent the letter.

There also is no update on the four people who sought medical attention.