The pilot of a plane which crashed into an office block in Austin, Texas left a note expressing his anger at federal tax authorities, police say.

美国德克萨斯州警方称，奥斯丁城一位飞行员驾驶着飞机撞到一座办公大楼，以此表示对联邦税务机构的愤怒。

debris¹ seemed to be the only thing left on some floors" width="226" height="170" src="/upimg/100219/4_010148_1.jpg" />
Twisted metal and debris seemed to be the only thing left on some floors

Police are linking the apparent（显然的，表面上的） suicide note left online to Joseph Andrew Stack, the man named as the pilot.

The note criticised the Internal Revenue Service - based inside the office block and declared: "Violence is the only answer".

Firefighters continue to search for one person who is still unaccounted for（下落不明的，未予解释的） .

'Leaping flames'

The single-engined Piper Cherokee airplane hit the second floor of the seven-storey building at 0956 local time (1556GMT).

It had taken off from nearby Georgetown airport in Texas, and did not file a flight plan, Lynn Lunsford of the Federal Aviation Administration said.

Heather Wills, from Austin, told the BBC that she was driving past when she saw the huge cloud of black smoke.

"As I got nearer I could see flames leaping out of（从……跳出来） the building - the flames were two storeys high. I could hear the glass windows shattering from the heat.

"My first thought was that it was a fire. The traffic was backed up all along the freeway."

Around 190 IRS employees work in the office complex and some were forced to climb out of windows after the plane burst into flames（突然着火，燃烧） .

Two people were taken to hospital, but it is not clear if they were seriously injured. There has been no official statement on the status of the pilot.

Grievance²

Police are also investigating whether Mr Stack set fire to his house before crashing the plane.

The message on the website apparently³ registered to and signed by Mr Stack speaks of having problems with the IRS（美国国税局） .

"Well, Mr Big Brother IRS man, let's try something different; take my pound of flesh（合乎法律的无理要求） and sleep well," the note reads.

Austin Police Chief Art Acevedo said there was no cause for concern and assured residents that it was an isolated⁴ incident.

The White House said the crash did not appear to be an act of terrorism.

White House spokesman Robert Gibbs said President Barack Obama had been briefed about the incident.

The Department of Homeland Security was investigating the crash, he added.

As a precaution（预防，警惕） , the North American Aerospace⁵ Defense⁶ Command scrambled⁷ two F-16 fighter jets from Houston, Texas, to patrol the area.