DORTMUND, Germany (AP) -- German authorities said Wednesday they are investigating "in all directions" after three explosions went off near Borussia Dortmund's team bus ahead of a Champions League quarterfinal match, injuring one of the soccer team's players.
German news media reports citing unnamed sources said a note found at the scene contained radical Islamic rhetoric but that police were unsure whether that was genuine or an attempt to throw them off the track. Federal prosecutors took over the investigation; they typically handle especially serious cases, including those in which a terrorist motive is suspected.
The first-leg match against Monaco was called off shortly before kickoff Tuesday evening following the blasts near the team hotel in suburban Dortmund, which authorities assume were a targeted attack. Players and police were preparing to go ahead with the rescheduled match on Wednesday evening, with heavy security in place.
Investigators were checking the authenticity of a letter claiming responsibility that they found near the scene, and were refusing to give any details of its contents, citing the ongoing probe. Police spokeswoman Nina Vogt told ZDF television that "of course our investigations have to go in all directions to begin with."
Die Welt newspaper and Sueddeutsche Zeitung reported online that the unsigned note made reference to Germany's participation in the military coalition opposed to Islamic State. German Tornado reconnaissance planes, based in Turkey, are taking part in a noncombat role. The papers said experts on Islam were reviewing the note to try to determine its authenticity.
Investigators were also probing statements found on the web that indicated a left-wing motive to punish the club for allegedly not opposing racism strongly enough, the dpa news agency reported.
Federal prosecutors didn't immediately say why they were taking over the investigation, but scheduled a statement for 1200 GMT.
Spanish defender Marc Bartra suffered injuries in the wrist and arm and underwent an operation Tuesday night. Police said an officer who was accompanying the bus on a motorbike was suffering from blast trauma and shock.
Borussia Dortmund president Reinhard Rauball said Wednesday's rescheduled match would be a challenge for the team.
"However, we expect and I am confident that the team will do its best and deliver a spectacle in the Champions League this evening," he said.
UEFA, European soccer's governing body, said security was being reviewed at all three Champions Leagues games on Wednesday. It urged fans to allow extra time for the possibility of tougher security.
By the end of Wednesday morning, about 40 fans had gathered outside the team's training ground, many in the club's distinctive yellow and black shirts.
As police waited in vans lined up in front of the screened-off training pitch, four young women drew "You'll Never Walk Alone" in black markers on yellow cards.
Annika Lentwojt, a 21-year-old engineering student, said she was in the stadium Tuesday when the match was called off but "always felt safe."
Lentwojt said she is confident Dortmund's players will be able to perform in the rescheduled match.
"I think the game or the score in the end is not that important," she said. "They will concentrate, they are professional players. It's not the main topic of the game today."
Peter Sobeck, a 55-year-old city planner who described himself as a lifelong Dortmund fan, said he was shocked that players were targeted in a relatively small city like Dortmund. The city, located in the densely populated Ruhr industrial region, has just under 600,000 inhabitants.
"I thought (in) these great cities, Paris or Munich or London, something like that, but in Dortmund, I never thought that," he said.
Dortmund is one of Germany's most popular teams and a regular contender for the Bundesliga title, which it last won in 2011 and 2012. It is in fourth place with six games left to play this season, 18 points behind leader Bayern Munich — Germany's dominant club of recent years.