DORTMUND, June 14: Police detained around 170 German and Polish soccer fans following clashes ahead of their World Cup Group A match on Wednesday in the worst outbreak of trouble at the tournament so far.

Around 100 German fans were rounded up and taken into preventive custody following skirmishes around the Alter Markt area in the centre of the city.

Riot police closed off the square to isolate the fans and then moved in to take large numbers of them away after a standoff during which bottles were thrown.

A Reuters reporter in the city said fans had hurled bottles and fireworks at police in another clash close to the square.

Police had earlier detained around 70 Polish fans some armed with metal batons.

At first the mood in Dortmund was largely friendly with boisterous groups of fans drinking beer in the sunshine, but it turned darker as a group of German skinheads wearing black T-shirts began to behave threateningly.

“Their tone had become very aggressive so we decided to move in to prevent the situation from escalating,” a spokesman said.

The Poles detained were “problem fans” known to police as potential troublemakers while others were carrying “dangerous objects” such as batons, police said.

A police spokeswoman said a number of the German fans who had been detained were also known troublemakers.—Reuters