Federal Prosecutors in the country also said they were investigating a possible "terrorist link" to the incident, which left Dortmund's Spanish defender Marc Bartra requiring surgery.

The three explosive devices used in the attack, which forced the postponement of Dortmund's UEFA Champions League quarter-final, first-leg clash with French club AS Monaco at Signal Iduna Park, contained metal strips, it has been confirmed.

The detained suspect is one of two alleged Islamic extremists who have become the focal point of the investigation.

Prosecutors said two letters were found at the scene, each claiming responsibility.

One of the letters reportedly referred to the terrorist attack on the Berlin Christmas Market in December and military operations in Syria, although its authenticity has not yet been confirmed.

Hello! As you can see I am doing much better. Thanks for all your messages! All my strength to my team mates, fans and to @BVB for tonight!

— Marc Bartra (@MarcBartra) April 12, 2017

Lead prosecutor Frauke Koehle said authorities had "considerable doubt" over the credibility of another letter, which gave a left-wing extremist motive for the incident.

"Two suspects from the Islamist spectrum have become the focus of our investigation," said Koehle.

"Both of their apartments were searched, and one of the two has been detained."

Dortmund's bus was hit by three explosions when devices believed to have been hidden in bushes were detonated close to the team's hotel, the L'Arrivee Hotel and Spa.

Bartra was taken to hospital and had surgery on his injured arm to repair a fracture and remove shrapnel following the incident.

The 26-year-old broke the "radial bone in his arm" and had "bits of debris lodged in his hand".

One of the metal pins from the bomb embedded itself in the headrest of one of the bus seats, prosecutors said, with Koehle admitting "we can talk about luck that nothing worse happened".

A Government spokesperson said German Chancellor Angela Merkel is "appalled" by the targeted assault on the Bundesliga club, who are preparing to face Monaco in the re-arranged first-leg later this evening.

Borussia Dortmund chief executive Hans-Joachim Watzke insisted they would not "bend before terror" but conceded it would be a difficult occasion for the players when they take to the field tonight.

He also praised the conduct of supporters, who were forced to evacuate the 80,000-capacity stadium following the attack.

Several Borussia Dortmund fans took to social media last night to offer accommodation for Monaco fans who had travelled to Germany for the match using the hashtag #bedforawayfans.

"We want to show that terror and hatred can never dictate our actions," he said.

"This is perhaps the most difficult situation that we have faced in the past decades.

"We do not just play for us today. We play for everyone - no matter whether Borussia, Bayer Leverkusen or Schalke supporters. 

"And of course we play for Marc Bartra, who wants to see his team win.

"I have to express a huge compliment to our fans, who have dealt with it very well, objectively, reasonably and solidly.

"It will not be easy to get that out of the mind. 

"I think the team will feel it on Wednesday."

Dortmund are due to face Monaco tonight amid an increased security presence in and around the stadium.

The match will kick off at 18:45 CET.