German police have detained a suspect over three explosions that rocked Borussia Dortmund's football team bus, according to prosecutors.
The roadside blasts on Tuesday went off minutes after the team bus had set off to a planned home Champions League game against French club Monaco, injuring defender Marc Bartra and one police officer.
Frauke Koehler, spokeswoman for the federal prosecutor's office, said on Wednesday that the investigation was examining a possible "terrorist link" after three identical letters were found at the scene of the explosions.
"An Islamist background appears to be possible," she said, noting that the letter demanded that Germany withdraw its deployment of Tornado reconnaissance missions in an international coalition fighting the Islamic State of Iraq and the Levant (ISIL) armed group, and close the US airbase in the western German town of Ramstein.
"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," Koehler said.
Al Jazeera's Dominic Kane, reporting from Dortmund, said there were updates about the devices that were used in the attack.
"Metal strips had been embedded into the explosives and some of that metal found its way into the bus that carried the players of the Borussia Dortmund team," he said.
Bartra underwent surgery on a broken wrist after he was hit by flying glass, Reinhard Rauball, the Borussia Dortmund president, said.
A policeman, who was on a motorcycle escorting the team bus, also suffered from blast trauma and shock.
The explosions had a radius of more than 100m, according to federal prosecutors, who said it was down to luck that no one else had been harmed.
The match, a quarter-final first leg, was rescheduled for Wednesday, as security was beefed up around Dortmund and in Munich, where Bayern Munich will take on Real Madrid.
Extra forces were deployed around team hotels and their buses will take designated safe routes to the stadiums.
The assault was described by Dortmund city's police chief as a "targeted attack" against the team, while Chancellor Angela Merkel said she was "horrified" by the "repugnant act".
Hans-Joachim Watzke, Borussia Dortmund's chief executive, vowed that his side "will not give in to terror".
"We will play not only for ourselves today. We will play for everyone ... we want to show that terror and hate can never determine our actions," he said.
Vadim Vasilyev, Monaco's vice president, said: "Football must not be taken hostage," and pledged that the quarter-final would go ahead.
In a show of solidarity, German Interior Minister Thomas de Maiziere will also attend the match.
Germany has been on high alert since a series of attacks last year, including the Christmas market truck assault in Berlin in December that claimed 12 lives.
Source: Al Jazeera and news agencies