Experts said the ruling, made last month and announced on Tuesday, was a win for human rights in the European Union newcomer, where nationalism has been on the rise. In 2005 Siderov's Attack party won fourth place in the general election and Siderov himself came second in the 2006 presidential election.
The Sofia court ruled Siderov had created an atmosphere of animosity towards ethnic Turks, who account for about 12 percent of Bulgaria's 7.6 million population.
The court said Siderov would be fined if he ignores the ruling.
Siderov had claimed the ethnic Turkish party, which is part of the ruling coalition, was illegal on the grounds it violated a rule against ethnic-based factions.
He had also called for the scrapping of Turkish-language TV broadcasts.
"For many Bulgarians this language is unpleasant ... People who spoke this language had exterminated, murdered, enslaved, and robbed the Bulgarian people for centuries," the court quoted Siderov's statements made between 2003-2005.
The Turkish Ottoman state ruled Bulgaria for about five hundred years until the late 19th century.
Orthodox Christians and Muslims in Bulgaria lived in relative harmony and unlike neighbouring former Yugoslavia, the country avoided ethnic clashes after the fall of Communism.
"The court ruling is very important because it shows that a politician of the highest rank, a member of parliament, can be convicted of discrimination and ethnic harassment," said a lawyer for human rights watchdog Helsinki Watch.
Commentators have said the rise of the Attack party was helped by a combination of voter apathy and discontent at persistent poverty, high-level corruption and organised crime.
Last Mod: 09 Nisan 2008, 18:08