A software engineer furious with the US tax agency launched a suicide attack by crashing his small plane into an office building housing nearly 200 employees.
The attack in Austin, Texas, set off a raging fire that sent the tax workers running for their lives.
At least one person in the building was missing and the pilot was presumed dead, authorities said.
Emergency crews later found a body in the wreckage of the building, but police would not say whether it was the pilot, identified by the FBI as Joseph Stack, 53.
Law enforcement officials said that before taking off yesterday, Stack apparently set fire to his house and posted a long anti-government criticism on the internet. It was dated yesterday and signed “Joe Stack (1956-2010)”.
In it, the author cited run-ins he had with the Internal Revenue Service and ranted about the tax agency, government bailouts and corporate America’s “thugs and plunderers”.
“I have had all I can stand,” he wrote, adding: “I choose not to keep looking over my shoulder at ‘big brother’ while he strips my carcass.”
The pilot took off in a single-engine Piper Cherokee from an airport in Georgetown, about 30 miles from Austin, without filing a flight plan.
He flew low over the Austin skyline before smashing into the side of the seven-storey, black-glass building just before 10am local time, with a thunderous explosion that instantly stirred memories of the September 11th attacks in 2001.
Flames shot from the building, windows exploded, a huge pillar of black smoke rose over the city, and terrified workers rushed to get out.
The Pentagon scrambled two F-16 fighter jets from Houston to patrol the skies over the burning building before it became clear that it was the act of a lone pilot. President Barack Obama was briefed.
At least 13 people were injured, with two reported in critical condition. About 190 IRS employees work in the building.
AP