A pilot furious with the US Internal Revenue Service (IRS) has crashed his small plane into a seven-storey building in apparent suicide.
A US law official identified the pilot as Joseph Stack. He left a note on a website where he vented his anger at the IRS and said violence "is the only answer".
The Texas building into which he crashed his plane on Thursday housed IRS offices.
Thick black and gray smoke was seen coming out of the second and third stories of the building as fire crews using ladder trucks and hoses battled the fire.
The IRS website said an office of its EP Team Audit Programme, which examines employee benefit plans, was located in the building.
Peggy Walker, an IRS revenue officer who works in the building, said she was sitting at her desk when the plane crashed.
"It felt like a bomb blew off. The ceiling caved in and windows blew in. We got up and ran," she said.
Lynn Lunsford, a federal aviation administration spokesman, said the agency was investigating but had no immediate information on the type of plane or how many people were on board.
Peter Knudson, the national transportation safety board spokesman, said an investigator from the board's Dallas office had been dispatched to the scene of the accident to start an investigation.
Federal law enforcement officials said they were investigating whether the pilot crashed on purpose in an effort to blow up IRS offices.
The pilot, found dead at the crash site, in his note on the website listed out his problems with the IRS.