Hundreds of protesters burned tyres and threw rocks at cops as they demonstrated against the burning of the Muslim holy book in Malmo, Sweden.
The riots sent huge plumes of thick, black smoke rising above the city last night.
Extremists had earlier burnt the Koran in reaction to the arrest of a far-right Danish politician.
Rasmus Paludan, leader of the extreme right-wing party Hard Line, had been denied permission to hold a meeting in Malmo.
He was stopped at the border in Sweden and was banned from the country for two years.
Regarding the reactionary riots, a Malmo police spokesperson said last night: “We don’t have this under control but we are working actively to take control.
“We see a connection between what is happening now and what happened earlier today.”
Police spokesman Calle Persson said they suspected Paludan was going to break the law if he was let into Sweden.
“There was a risk that his behaviour… would pose a threat to society,” he said.
Following his arrest, supporters burned the Koran during rallies, and three people were arrested for inciting racial hatred.
Paludan caused controversy last year when he burned a copy of the Koran surrounded by bacon.
He posted a message to Facebook after being arrested.
“Sent back and banned from Sweden for two years. However, rapists and murderers are always welcome,” he wrote.