The Federal Aviation Administration’s Minneapolis office was evacuated Tuesday afternoon after a letter that contained a suspicious substance was found.

Four people were hospitalized as a precaution, FAA spokeswoman Elizabeth Cory said.

Several agencies, including the Department of Homeland Security, were investigating, she said. The FAA is cooperating with that inquiry.

Cory said the office, at 6020 28th Av. S., houses employees involved in aircraft certification, security, pilot licensure and regulatory compliance, as well as airline and airport regulatory compliance.

“Air traffic control functions are not located in this building and have not been affected,” the statement read. Few other details have been released.

Cory said she didn’t know how many workers were evacuated. No one was at the building late Tuesday afternoon.

Several news reports said the letter was found early Tuesday afternoon.

Tim Burke, spokesman for Allina Health Emergency Medical Services, confirmed that four people were taken to HCMC but said he had no further information. A hospital spokesman said Tuesday evening that he had no information on their conditions.