German investigators on Wednesday detained an Islamist suspect over three explosions that rocked Borussia Dortmund's team bus, prosecutors said, confirming that the probe was examining a possible "terrorist link".
The roadside blasts left Dortmund's Spanish international Marc Bartra and a policeman injured, with the bombs "containing metal pieces" detonating minutes after the team bus set off to a planned Champions League game against Monaco on Tuesday night.
The blast had a radius of more than 100 metres (yards), federal prosecutors said, adding it was lucky the toll was not higher.
The match was belatedly held Wednesday, with Monaco claiming a 3-2 win in front of a packed stadium as a defiant Dortmund team vowed it won't "give in to terror".
Security was ratcheted up around Dortmund for the match, as well as in Munich where Bayern Munich were taking on Real Madrid.
"Bartra! Bartra!", chanted supporters just before the quarter-final, first leg tie began in Dortmund, in support of the defender who was hurt by flying glass.
Federal prosecutor's office spokeswoman Frauke Koehler said the probe was examining a possible "terrorist link", after three identical letters were found at the scene.
"An Islamist background appears to be possible," she said, noting the letter demanded that Germany withdraw its Tornado reconnaissance missions in the international coalition against the Islamic State group, and close the US air base in Ramstein, western Germany.
"Two suspects from the Islamist spectrum have become the focus of our investigation. Both of their apartments were searched, and one of the two has been detained," she added.
Local media identified the suspects as a 25-year-old Iraqi and a 28-year-old German.
At least one of the two could have been close to the scene at the time of the explosion, reports said, quoting unnamed security sources who nevertheless urged caution on linking the individuals to the assault.
- 'Absolutely shocking' -
Chancellor Angela Merkel said she was "horrified" by the "repugnant act", which Dortmund city's police chief Gregor Lange described as a "targeted attack" against the team.
Germany has been on high alert since a series of jihadist attacks last year, including a Christmas market assault in Berlin.
Tuesday's explosives detonated minutes after the Dortmund team bus pulled away from the squad's hotel.
Bartra underwent surgery on a broken wrist, Dortmund president Reinhard Rauball said.
A policeman, who was on a motorcycle escorting the team bus, suffered trauma from the noise of the blasts.
"The bus turned on to the main road, when there was a huge noise -- a big explosion," Dortmund's Swiss goalkeeper Roman Burki told Swiss media.
"After the bang, we all crouched down in the bus. We did not know if more would come." Some players hurled themselves to the ground, he said.
Underlining the severity of the blasts, prosecutors said a piece of metal shrapnel had lodged in the head-rest of a bus seat.
Despite the shocking incident, Dortmund's chief executive Hans-Joachim Watze said returning to the pitch a day after was the right thing to do.
"For the team, it was an absolutely shocking experience," he said.
"The question is how do you react to it and I think that (playing) sends the right signal, but I know that it will be painfully difficult for the players," he said.
Interior Minister Thomas de Maiziere, who attended Dortmund's match on Wednesday, said the "fascination" surrounding football drove terrorists to try and disrupt it.
"That's why it's right that we do as much as we can to protect it, and not allow criminals to take the fascination away from us."
- 'Beautiful moment' -
But Dortmund coach Thomas Tuchel complained that the team had not been consulted over the decision to play.
"It came down to 'tomorrow, you’re playing', he said.
"It was a somewhat powerless feeling," he added. "Each player had the right to start with a somewhat queasy feeling."
The announcement that Tuesday's game was postponed was only made to the stadium, packed with fans, about 15 minutes before kick-off.
Merkel praised supporters for their "calm" behaviour and the host side for their hospitality, after some Dortmund fans took in stranded Monaco supporters for the night.
Boris Marchi, 26, who was wearing both the red and yellow scarf of his club Monaco as well as the yellow and black of Dortmund, said he was offered lodgings by a German supporter.
"It was really a beautiful moment," he told AFP.