Police officers stand guard near the site where German soccer team Dortmund's bus was damaged by explosions in Dormund, Germany, on April 11, 2017. (Xinhua/Ulrich Hufnagel)

FRANKFURT, April 11 (Xinhua) -- Explosions hit the team bus of German soccer team Borussia Dortmund ahead of its first game of UEFA Champions League quarter-final against AS Monaco Tuesday, injuring one player, local police said.

Dortmund police said the real background of the blasts was still unclear but assumed that the German soccer team was targeted in the incident.

A letter was found near the site of explosions, which claimed responsibility for the incident but its authenticity couldn't be confirmed, according to authorities.

So far no evidence indicated that the explosions were of "terrorist" nature, German news agency DPA reported, quoting security sources.

Soon after the incident, Borussia Dortmund said its Champions League match against Monaco scheduled for Tuesday evening was put off until Wednesday.

The explosions triggered by three explosive subjects hit Dortmund team's bus in the district of Hoechsten of the western German city of Dortmund, as the team set off from their hotel to the stadium Signal Iduna Park.

Dortmund defender and Spain international Marc Bartra was injured and in hospital, the club said.