+++ Explosion hits Dortmund bus - live updates +++

- Three explosive devices detonated near Borussia Dortmund's bus on Tuesday as it was leaving the team hotel on the way to the Champions League quarterfinal match with French side Monaco. The game has been postponed until Wednesday.

- Spanish defender Marc Bartra was injured in the explosion and is undergoing surgery for injuries to his wrist and lower arm. The bus's windows were shattered in the attack.

- Police say this was a targeted attack using "serious explosive devices" which could have been placed in a hedge near a car park. They also found a letter near the scene, which is being investigated.

Read the full report on the Dortmund bus explosion here

All times in UTC (Coordinated Universal Time)

21:45 The press conference has now wrapped up. We learnt that they believe this to be a targeted attack, that they found a letter claiming responsibility at the scene that is yet to be authenticated and that Marc Bartra will need surgery on his wrist and lower arm.

21:38 While the legitimacy of the letter is yet to be established, police say the writer claims responsibility for the attack.

21:30 This tweet from the local police explains that a letter was found in the vicinity of the attack and its authenticity is under investigation.

21:28 Borussia Dortmund's representative at the press conference confirms that Marc Bartra is undergoing surgery on his injured wrist and lower arm. It seems his injury is more serious than first thought.

21:23 The police also make it clear that security will be stepped up for the re-scheduled game on Wednesday. They add that they are searching for a car with a foreign registration plate.

21: 20 The police press conference is underway. They say that they assume the attack was targeted but the motive is currently unclear and nothing can be excluded at this stage.

21:11 Monaco have issued a statement that reads: “Faced with this difficult situation, AS Monaco wishes to express its full support for the whole Borussia Dortmund team and club.”

21:05 The police press conference is due to start any minute. Here's what they know so far.

20:38 Dortmund police will hold a press conference in about 20 minutes time. 

20:28 Werder Bremen midfielder Serge Gnabry is one of many footballers to pass on his best wishes to the Dortmund players.

20:07 Dortmund police have told press agency DPA that, as yet, there is no indication that the three explosions are terror-related. But they have said it was "an attack with serious explosive devices" and that the devices could have been placed in a hedge near a car park.

20:02 Borussia Dortmund goalkeeper Roman Bürki was sitting next to Marc Bartra on the bus when it was rocked by an explosion.  He told Swiss newspaper 'Blick' that "there was a huge bang, literally an explosion" that sent glass flying about.
19:52 In the middle of all the negative news, came this nice gesture from Dortmund. 

19:44 Borussia Dortmund CEO Hans-Joachim Watzke has just wrapped up a Facebook Live on the club's official page. He said Marc Bartra has been treated in hospital for cuts on one arm and hand. He added that police have told him explosive devices were hidden in a roadside bush on a public road just outside the team hotel.

19:41 DW's Michael da Silva was in Dortmund for the game, here's what he just told DW News.

19:35 Former Dortmund midfielder Ilkay Gündogan has also expressed his disbelief at the incident: "I can't believe it," he tweeted. "I hope everyone is fine." 

19:29 Martin Schulz, leader of Germany's Social Democrats (SPD) has reacted to the explosion. "I'm shocked," he wrote on Twitter. "Best wishes. And a safe journey home to all fans."

19:20 Borussia Dortmund CEO Hans-Joachim Watzke says Marc Bartra's injuries are "nothing life-threatening."

18:52 One of our reporters has just spoken to an eyewitness. The person told DW that he was at the hotel where Borussia Dortmund was staying when he witnessed the explosion.   

"The BVB bus was still there and was waiting for Thomas Tuchel [Dortmund coach]. Then the bus started to drive to the stadium. After a few moments a huge explosion happened. I was sitting in the car. The whole car was shaking." 

The man estimated he was about 30 meters (100 feet) behind the bus when this happened. He used the words "crazy" and "heavy" to describe the situation.

18:45 Borussia Dortmund have just tweeted to confirm that the person injured in the explosion was Spanish defender Marc Bartra. The club say he's already in hospital and have wished him all the best.

18:43 A police spokesman has just confirmed that the explosion happened shortly after the bus left the hotel. Several windows were shattered and one passenger was injured. 

18:40 The supporters in the stadium now know the news but have been asked to stay inside for the time being for security reasons.

18:34 Dortmund police say there were three explosions around the team hotel.

18:30 It's now been confirmed that tonight's match has been postponed until Wednesday.

18:29 Here's a statement from local police: 

"In the run-up to the Champions League match of BVB against AS Monaco, there was an explosion near the BVB team bus shortly after 7pm. The location of the event is Wittbräuckerstraße/Schirrmannweg in Dortmund-Höchsten.

"According to current knowledge the windows of the bus (whole or partial) were shattered and one person was injured. It is not yet possible to say exactly what the explosion was or exactly where something exploded."

18:25 It's being widely reported in German media that Dortmund defender Marc Bartra was injured in the explosion.

18: 21 There will be a decision on whether the game will go ahead in about 10 minutes.

18:18 Both Dortmund and local police have tweeted confirmation of the incident which happened outside the team hotel shortly after 17:00. While reports suggest no players have been injured, at this stage it is unclear whether the game will go ahead. 

mp/kms (SID, dpa)