Borussia Dortmund fans claim their singing was drowned out by a high-frequency speaker at the defending Bundesliga champion's match at Hoffenheim on Saturday.

The Schwatzegelb Dortmund fan forum appealed for photographic or video evidence Monday, as Kicker magazine reports of a complaint made to police.

Police spokesman Harald Kurzer told Kicker ''we received a complaint from a fan in Pforzheim today. We're looking into a suspected case of personal injury.''

German daily Bild showed pictures of a speaker placed strategically under the visiting fans' block.

Hoffenheim claimed a fan was responsible, saying in a statement that ''allegations of a deliberate action from the host are unfounded.''

Dortmund lost the game 1-0.