"The chancellor was last night, like people in Dortmund, like millions everywhere, appalled by the attack on the BVB team bus," said Seibert in a press conference, "One can only be relieved that the consequences were not worse."

Three explosive devices placed by the roadside next to the bus transporting the football players to the match against AS Monaco went off on Tuesday night. Spanish defender Marc Bartra suffered injuries to his arm and wrist in the explosion. A police officer on a motorcycle accompanying the bus suffered acoustic shock and trauma.

"Our thoughts are with the two injured and we wish them a complete recovery," said the spokesman, adding that Merkel had telephoned Dortmund's Managing Director Hans-Joachim Watzke to wish the team and the fans well.

German Federal Prosecutor's Office has been investigating the attack and two claims have been found. A letter of responsibility was found close to the bombing location, according to German media sources, claiming the attack was orchestrated by Islamic State supporters to revenge the German army's operations in Syria. The other claim posted online linked the attack to anti-fascist activists.

Authorities said both claims cannot be easily associated with the attackers. There is much reason for skepticism on both accounts.