The suicide bomber who killed himself in Beijing's Tiananmen Square was a "paranoid madman" with a long-running grievance over a fine for tax evasion, a Chinese official said Wednesday.

The official said the aggrieved farmer had made a series of protests over a 1997 fine for not paying his taxes, and that in January he took off all his clothes in front of Tiananmen Gate.

The man blew himself up on Tuesday afternoon in the square, injuring a South Korean tourist and causing a massive security alert in the heart of Beijing close to the government headquarters.

A spokesman for the South Korean embassy said the 32-year-old tourist underwent surgery on Tuesday to remove fragments of shrapnel from both his legs, and would remain in hospital for several days.

The bomber, identified as Li Xiangshan, had been caught several times riding the train to Beijing from his home in central Hubei province without paying the fare, and once in May 1999 he was found to have explosives on him.

Each time he was sent back to Hubei for psychiatric evaluation, and that tests in January 1998 and Janaury 1999 found that he was "paranoid and insane, and not fit for any kind of duties".