Two people were arrested and some injured as supporters of Volen Siderov's Ataka party clashed with Muslims on May 20 2011 as the ultra-nationalists protested against the loudspeakers calling the faithful to prayer at the Banya Bashi mosque in central Sofia.
This is the latest in a series of protests which started some years ago against the loudspeakers, but Ataka has revived its campaign in the run-up to Bulgaria's autumn 2011 municipal and presidential elections, in which Siderov has said he will be a candidate.
Scuffles broke out after one of the Ataka protesters tried to steer a column towards Muslims taking part in Friday prayers, Bulgarian National Radio said.
Ataka supporters shouted "Ataka","Bulgaria", "Turks out" and "janissaries," eyewitness reports said. Protesters threw stones and bottles at the mosque.
After the brawl broke out, two Ataka supporters were arrested.
Siderov alleged that one of the Muslims had thrown a stone at an Ataka MP, Denitsa Gadzheva, but had not been arrested. Gadzheva and another participant in the protest were taken to hospital by ambulance.
Five police officers and five Muslims were injured, the Interior Ministry said.
Siderov alleged that the police were biased, and called them a "janissary corps", a reference to the Ottoman-era practice of Bulgarians being taken into service of the sultan.
Local news agency Focus said that after the clash at the mosque, Ataka supporters headed towards the Parliament building.
Ivailo Ninov, one of the protest organisers, said that the event had been directed against the use of loudspeakers to sound the call to prayer, and not against Muslims. He said that residents of the area had joined the protest in support.