Borussia Dortmund's team bus was the victim of what was believed to be a targeted bomb attack on Tuesday night before the Champions League clash with Monaco, as a letter found outside the hotel “[taking] responsibility for the act” was found.

Three explosions went off next to Dortmund’s team bus as it travelled to the Westfalenstadion for the first-tie of the club’s Champions League match against Monaco.

The Spanish player Marc Bartra was seriously injured in the incident and later underwent an operation on a broken wrist. The match between Dortmund and Monaco was immediately called off and rescheduled for Wednesday.

Borussia Dortmund bus blasts injure player Marc Bartra

In a press conference following the attack, the police chief for the city of Dortmund confirmed that the team bus was the intended target for the “serious explosive devices” which struck the coach, although reiterated it was not yet clear who was responsible for the attack.

“At this time, it is still not clear what the real background to this act is,” Dortmund police chief Gregor Lange told a news conference.

“We must start from (the position this was) a targeted attack on BVB's team. Strong police forces are in operation.

“We also have explosive detection dogs in use and decided to search the scene from the air. At the present time it is not clear what the background of the act is.”

Police stand near the team bus after the attack (Getty)

The police earlier said in a statement that the explosives “may have been hidden in a hedge near a parking lot”.

A prosecutor added that a letter found outside the hotel the team bus was departing from when the explosions happened “takes responsibility for the act”.

However, prosecutor Sandra Luecke said authorities won't give details of the unauthenticated letter at this stage, citing the ongoing investigation.

Borussia Dortmund bus explosion Show all 20 1 /20 Borussia Dortmund bus explosion Borussia Dortmund bus explosion Borussia Dortmund bus explosion A number of Dortmund players have admitted they have struggled to cope following a bomb attack on their team bus, which left defender Marc Bartra hospitalised. Bongarts/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund player was injured following explosions near the team bus ahead of the Champions League quarterfinal match against Monaco. Bongarts/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion North Rhine-Westphalia police spokesman Gunnar Wortmann told The Associated Press Tuesday that there were "three explosions near the team bus as they left the hotel to go to the stadium" and that "there was one player injured inside and damage to a window." AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund said the player was "in safety" and that "there is no danger in and around the stadium." AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion In a statement, police say there was an explosion after 7 p.m. local time. AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion The chief executive of a German soccer team Borussia Dortmund says player Marc Bartra was injured on the arm and hand when three explosions went off near the team bus. AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund Chief Executive Hans-Joachim Watzke said the injuries to the Spanish defender Tuesday night are "nothing life-threatening." Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund police spokeswoman Nina Vogt says investigators do not yet know the source of the explosions that went off as the team was preparing to leave their hotel for a match against Monaco. Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion The chief executive of German soccer team Borussia Dortmund says police informed him that the explosives that went off near the team bus were hidden by the exit of a hotel and detonated as the bus passed. Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Borussia Dortmund goalkeeper Roman Buerki says the team bus had just pulled out of a hotel driveway at about 7:15 p.m. when it was rocked by an explosion. Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Buerki told Swiss daily Blick on Tuesday night that "there was a huge bang, literally an explosion" that sent glass flying about. Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Bongarts/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Police in the German city of Dortmund say investigators "are working on the assumption" that the explosions that rocked a professional soccer team's bus were caused by "serious explosive devices." Bongarts/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund police said the devices that went off near the bus as German team Borussia Dortmund was leaving its hotel for a match Tuesday night "may have been hidden in a hedge near a parking area." AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion The Champions League quarterfinal first leg game between Dortmund and Monaco was called off and rescheduled for Wednesday. AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion The police chief for the German city of Dortmund says it's not clear yet who was behind the explosions that rocked a bus carrying the Borussia Dortmund soccer team and left a player injured. AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion A spokesman at the already crowded stadium informed fans of the cancellation, saying that "there is no reason for panic here at the stadium." AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Bongarts/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion Dortmund Police Chief Gregor Lange told reporters late Tuesday that police decided at an early stage that the soccer team was the target of the explosions and are not excluding any possible angles in their investigation. AFP/Getty Images Borussia Dortmund bus explosion Borussia Dortmund bus explosion A prosecutor says a letter found outside the hotel the team bus was departing from when the explosions happened "takes responsibility for the act." AFP/Getty Images

The police were also asked at the press conference about rumours of an alleged blackmail plot against the club. “That’s the first we’ve heard about that,” Grange replied.

The Uefa president Aleksander Ceferin later said that he was “deeply disturbed” by events in Dortmund and backed the decision to reschedule the match.

He said in a statement: “I was deeply disturbed by the explosions which occurred in Dortmund.

“The decision taken to postpone the Uefa Champions League match between Borussia Dortmund and AS Monaco was the correct one since we must always prioritise the safety and security of all fans, team officials and players.”

Ceferin said he was 'deeply disturbed' by the attack (Getty)

Fifa president Gianni Infantino also published a statement, saying: “The thoughts of every one of us at Fifa are with the people of Dortmund, and the fans of both Borussia Dortmund and Monaco following today's troubling events.

“We are closely monitoring the condition of BVB's Marc Bartra, and wish him a speedy recovery from his injuries.