Frightened Muslim residents threw up barricades as more than 1,000 students--many waving Serbian flags and the banner of Serbian extremists--rampaged through the center of Brcko.
U.S. troops stationed on the outskirts of the city did not intervene. Bosnian police stood by as the students pelted them with stones, eggs and tomatoes.
Brcko long has been considered one of the most serious potential flashpoints in Bosnia-Herzegovina since the Dayton peace agreement ended the country's 31/2 year ethnic war in 1995.
Bosnian Serbs overran the town during the war and expelled Muslim and Croat residents. The Dayton peace conference failed to resolve who would control the town.
Last year, the international overseers who effectively govern Bosnia decreed that Brcko would be under multiethnic administration. The deal angered both Bosnian Serbs and Bosnian Muslims who insisted on exclusive control.
The unrest erupted Friday when a group of Serb students beat up a Muslim student after classes, Serb and Muslim residents said. Serb and Muslim students share the same school buildings but attend class in two shifts.
``There was a fight on Friday and this Muslim was a bit injured,'' said Slavka Petrovic, a 17-year-old Serb student. ``Then the Muslims organized themselves on Monday and we organized ourselves on Tuesday.''
In the wake of last week's fight, Bosnian Muslim students agitated for better security while the Bosnian Serbs demanded separate schools.
On Wednesday, however, the Bosnian Serb students expanded their demands, insisting that the town be cleared of Muslims and restored to Bosnian Serb control.
Two young men who led the crowd carried the banner of the hard-line Serb Democratic Party--founded by Bosnia's top war-crimes suspect, Radovan Karadzic.
Speaking to reporters later Wednesday, student Miodrag Krunic said certain demands must be met before they will stop protesting. In addition to the separate high schools, they asked for a separate university and the right to use Serb symbols everywhere.
They also protested their own politicians' tolerance of increased rights for Muslims.
Semso Muminovic, who teaches at the school where the trouble began, claimed that a fellow teacher who belongs to another extremist group--the Serb Radical Party--was behind the unrest.
Local radio stations quoted the school's principal as saying the teacher and other Radical Party members have been urging students to demonstrate. Muslims said the extremists organized two busloads of soccer fans from the Bosnian Serb-held town of Bijeljina to join the protests.
The reports could not be confirmed because turmoil in the town made it impossible to find Bosnian Serb officials.
Mirza Ribic, 16, a Muslim student, said a Radical Party teacher tore the Bosnian national emblem from the school building and replaced it with a picture of Serbia's patron saint, St. Sava. The Muslims then burned a Serb flag in retaliation, he said.
``Then each time we met, they provoked us,'' he said. ``I'm not going to school anymore. Better that than become an invalid.''
A spokesman for the chief international overseer, Wolfgang Petritsch, condemned the violence and accused extremists of raising tensions before national elections next month.
Under Bosnia's 1995 peace agreement, the country is divided into two autonomous regions, one run by Bosnian Serbs and the other shared by the country's Muslims and Croats. A NATO-led peacekeeping force was installed to help enforce the peace.