Sources told the BBC that the demonstrators in Nasiriya were now "in control" of the situation in the city and were "chasing the police in the streets and alleys."
Iraq's anti-government protests have been directed mainly at the country's political leaders.
But many of those taking part have also expressed anger at Iran's influence over Iraq's internal affairs, which has steadily grown since the US-led invasion that toppled Saddam Hussein in 2003. On Wednesday, the Iranian consulate in the city of Najaf was attacked.
