Germany arrests 1, eyes Islamic extremist motive in Dortmund

Police said they were working on the assumption that the blasts were directed at the Dortmund team and caused by "serious explosive devices", which may have been hidden in a hedge near a auto park.

She said investigators are examining the authenticity of what was written in the letter, but wouldn't reveal more about its contents, citing the ongoing investigation.

The team bus was severely damaged in the blast, which police are treating as a terrorist attack "based on the facts of the crime", however the exact motive remains unclear, according to a police statement.

UEFA said "security procedures will be enhanced accordingly wherever needed".

German authorities arrested a suspected Islamist on Wednesday in connection with an attack on a bus carrying players of one of the country's top soccer teams, a spokeswoman for the Federal Prosecutor's Office said.

In addition to Dortmund's rescheduled tie with Monaco, Wednesday will also see Atletico Madrid host Leicester City and Real Madrid head to Bayern Munich, with UEFA being moved to reconsider safety arrangements for the three games.

Dortmund player Marc Bartra was injured in the explosions and has had surgery on this arm and wrist.

Lange said a further "suspicious object" was found at the scene, but it does not appear to have been another explosive device.

One suspect has been detained, and another is being investigated.

Watzke admitted the attack, which left defender Marc Bartra with a broken wrist, had left the team needing to come to terms with the "incomprehensible" very quickly.

Dortmund police said security would be tightened at today's match, with a major deployment of officers ahead of the kickoff at 6.45pm.

The Chancellor of Germany, Angela Merkel, had earlier offered Dortmund words of encouragement after getting in touch with the club to express her support.

The explosives detonated minutes after the Dortmund team bus pulled away from the squad's hotel and headed for the stadium.

"I think the game or the score in the end is not that important", she said.

"We want to show that terror and hatred can never determine our actions".

Manchester United attacker Mkhitaryan, who made 140 appearances for the German club over three seasons, also took to social media to share his support to Bartra and his ex-club.