Forty "problem fans" of Poland have been detained by Dortmund police ahead of their national team's second World Cup Group A match against old foes Germany on Wednesday.

The arrested Poles, almost of who are known soccer hooligans, were pointed out by Polish police in town for the game, with four of them, with knives, arrested near the match site Westfalenstadion and the other thirty-six near the city center.

Dortmund police spokesman Georg Blaszyk said that the action showed they're determined against any turbulence surrounding the tournament.

"We are well prepared for potentially violent groups traveling to Germany," Dortmund's police said in a statement Wednesday.

Fears toward a fan violent have overshadowed Wednesday's showdown between Germany and neighbor Poland for months, especially as about 100 Germans and Poles brawled near the border in November.

"We view this as a potentially explosive match," said the Dortmund authority. "We will have extra police on duty and will be vigilant. Up to now there is nothing to suggest there will be attacks although of course that does not mean nothing will happen."

There might be up to 300,000 Poles traveling to Germany during the tournament and Polish police have been working with the German counterpart to identify and weed out suspects to prevent possible troubles.

After Friday's 2-0 defeat of Poland by Ecuador at Gelsenkirchen, however, Polish fans showed good behavior and raised no violence nor problem.