Preliminary tests did not reveal any “biological agents of concern” inside a letter that prompted Tuesday’s evacuation at the Federal Aviation Administration’s Minneapolis office, according to the FBI.

Michael Kulstad, a spokesman for the FBI in Minneapolis, said Wednesday that state Health Department technicians were conducting additional tests “out of an abundance of caution.”

It is still unclear what was in the letter, which also led to the precautionary hospitalization of four people.

HCMC did not immediately respond to an inquiry for further information on those individuals.

In an earlier statement, the FAA said that the office, at 6020 28th Ave. 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 at the building and were not affected, the FAA said.

On Wednesday, the FAA referred all questions to the FBI.