Several hundred people took to the streets of Australia's largest city on Saturday, some throwing rocks and bottles during clashes with police, as anger over a film that insults the Prophet Mohammad spreads.
A demonstration that began with about 200 people outside the U.S. consulate in Sydney swelled to more than twice that number, with protesters appearing to catch police off guard as they marched through the centre of the city.
Some of the chanting protesters carried placards reading "Behead all those who insult the Prophet".
Several streets, usually thronging with weekend shoppers, were blocked off by police as the protest grew. Police, many wearing anti-riot equipment and some on horseback, used dogs and chemical sprays as they tried to control the protest.
Reuters Television pictures showed one policeman with a head injury being bandaged by paramedics. Police refused to confirm how many protesters had been arrested or if any of their officers had been injured.
A spokesman for paramedics said four people had been taken to hospital, none of them injured seriously.
A police spokesman said the protest was being monitored, with demonstrators gathering in a central Sydney park. A Muslim leader addressed the protesters in the park, calling for calm.
Australia, a staunch U.S. ally with troops still fighting in Afghanistan, has a Muslim population of about 476,000, or 2.2 percent of the population, according to 2011 census figures.