An apparently disgruntled man crashed a small plane into a federal building housing US tax offices in Austin, Texas on Thursday in what local officials said was likely a deliberate attack.

 Two people were taken to the hospital after the crash that set ablaze the seven-storey building, Austin fire officials said. The pilot, identified by law enforcement sources as Joseph Andrew Stack, was found dead.   

The incident renewed fears of domestic terrorism and gaps in security for private aircraft. The White House said it had no reason to believe there was a link to foreign terrorism and that President Barack Obama was briefed on the situation.   

It was probably "a deliberate attack by one individual acting alone," Austin Police Chief Art Acevedo said, downplaying the threat of more attacks.

US Representative Michael McCaul of Texas called it "a deliberate and intentional attack against a federal building."    

A rambling note posted on the Internet and signed "Joe Stack" spelled out problems he had with the Internal Revenue Service tax agency. A law enforcement source said authorities were investigating the note.

"Well, Mr. Big Brother IRS man, let's try something different; take my pound of flesh and sleep well," the note said. It was not possible to independently determine the authenticity of the note, dated Feb 18, or its authorship.

In the note, Stack complained that he ran afoul of US tax laws when he failed to file a return after not earning any income one year. He also said in the note that he had trouble resolving some undocumented income.

CNN reported the pilot had set his own house in Austin on fire before taking off in the plane and crashing it into the building at about 10 am CST (1600 GMT). The authorities were also investigating that report, the law enforcement source said.

The plane, identified by the Federal Aviation Administration as a single-engine Piper Cherokee, took off from the airport in nearby Georgetown and was flying under rules that did not require the pilot to maintain contact with air controllers.

A Piper aircraft was registered to Joseph Stack under a Lincoln, California, address, according to the FAA's registry. In the note, Joe Stack said he had moved to Austin from California.

The damaged building housed IRS offices with about 190 employees, including the criminal investigation division as well as auditors and tax collectors, according to agency officials. It sits across the street from an FBI office.
   
As a precaution, two F-16 fighter aircraft were scrambled after the crash and patrolled above the Texas state capital, according to North American Aerospace Defense Command which is responsible for guarding US airspace.

US Treasury Secretary Timothy Geithner, whose department includes the IRS, expressed concerns about the incident during an appearance in North Carolina. "We are closely monitoring the situation," he said, adding the crash "is of deep concern to me."  - Reuters