Anti-Isis (Islamic State) protests organised by Kurdish nationals in a number of German cities have erupted into violent clashes, with radical Muslims armed with knives and brass-knuckles.

The demonstrations in the city of Hamburg and the town of Celle deteriorated into violence, forcing German police to request reinforcements to restore order.

The clashes occurred on Tuesday after 80 Kurdish protesters occupied Hamburg's main train station for an hour before leaving voluntarily, according to local police.

Approximately 500 Kurdish demonstrators marched through Hamburg, causing damage to a number of cars and Turkish snack bars. Fourteen Kurdish protesters were arrested.

A few hundred Kurdish protesters then gathered at a mosque near the train station before they were attacked by a group of 40 armed supporters of IS. Four people were taken to hospital with stab wounds following the incident.

Police used water cannons, batons and pepper spray to bring the unrest under control while both sides threw stones and bottles in an attempt to break police lines and attack the other.

The clashes in Celle occurred a day earlier, with 100 Kurds and 100 Muslims brawling until police calmed the situation.

Protests against the Islamic State have been organised in cities and towns across Germany such as Hannover, Oldenburg, Wolfsburg, Bremen, Gottingen and Kiel.

Kurdish refugees are protesting against the Islamic State's offensive on Kurdish communities in northern Iraq and northern Syria, particularly the city of Kobani, where over 150,000 Syrian-Kurds have fled into Turkey.

In the city, American airstrikes have pushed IS militants back from some districts that they had captured after a three-week fight for the city.

Since the Islamic State (also known as Isis) raised their black flag on the eastern side of the town, raids on the Sunni Islamists have multiplied.

According to the Syrian Observatory for Human Rights, a British-based monitoring group, militants "withdrew overnight from several areas in the east of Kobani".