​A letter said to 'claim responsibility' for Tuesday's bomb attack on the Borussia Dortmund team bus has been discovered along with a number of other suspicious items near the scene of the explosions, according to German prosecutors. 

Three suspected bombs were detonated when the Dortmund bus left their hotel for the Champions League quarter-final first leg meeting with Monaco at the Signal Iduna Park. 

Defender Marc Bartra was understood to have been taken to hospital with injuries to his wrist and arm, whilst the match was subsequently postponed and rescheduled for Wednesday evening. 

With German police now investigating the alleged attack, the ​Mirror report that prosecutors have revealed that a letter 'claiming responsibility' for the blasts was found near the scene, as well as a number of other 'suspicious items' which were located around Dortmund's hotel. 

Efforts are now being made to verify the claims made in the letter, as police refuse to release further details regarding the other suspicious items that were discovered. 

Gunnar Wortmann, a police spokesman, said in the hours after the attack: "We will be working throughout the night to discover who was behind this attack. All police and vehicles in Dortmund have been mobilized.

"Three explosions detonating at the exact moment the bus passed by suggest a sophisticated expertise in both bomb building and detonation - perhaps using a mobile phone or a garage door-opening device."

It is not thought that the attack is linked with either set of fans as police now explore the likely possibility that it was terror related. 

Spanish newspaper ​AS report that investigators are probing possible radical Islamist links, although there has not yet been any official confirmation of who was behind the bombing.