Hazardous material crews were called to an IRS building in Ogden, Utah on Monday less than two weeks after a man deliberately crashed his private plane into an Austin, Texas building that housed IRS workers, the U.S. tax agency confirmed.

"At approximately 11:15 AM MST, we detected an unknown substance at the IRS Campus," the agency said in a statement. "A local Haz-Mat team was dispatched and standard procedures for responding to such an incident were implemented. At this point we cannot provide additional details because we are continuing to assess the situation."

A law enforcement official told Fox News "some kind of suspicious substance" was found inside a piece of mail, which may have been a tax return or letter. At least two people could be seen being removed on stretchers from the building.

The FBI was called to the scene and reporters were not allowed into the building after the incident, The Standard-Examiner reported.

Later, showers were being used to deal with "a possible chemical situation," according to the local ABC affiliate. The news station alluded to dispatcher calls that indicated a powder may have been found in the mail at the facility.

Responding to claims by an official with the U.S. Postal Inspection Service that the substance was not hzardous, an IRS source told Fox News that testing had not yet been completed.

"Nothing has been confirmed to be hazardous, but we haven't received the final analysis yet," the insider added.

The Ogden facility is part of a larger IRS campus that employs approximately 7,000 people in the area, according to an article last month in the Salt Lake Tribune. The IRS is one of the top 15 employers in the state.

Ogden is approximately 40 miles north of Salt Lake City. It is home to Weber State University.