German Bundesliga club Borussia Dortmund's team bus was the target of an attack in three explosions ahead of their Champions League tie against Monaco yesterday, police said in Dortmund, Germany.

"At the present moment it is still unclear what the concrete background is to this act," Dortmund police chief Gregor Lange told a news conference.The devices exploded as the team bus left the squad's hotel some two-and-half hours ahead of the first-leg quarter-final match.

A note claiming responsibility for the attack was found near the scene and its authenticity was being "intensively examined", prosecutor Sandra Luecke said.

Dortmund's Spanish defender Marc Bartra was taken to hospital with a fracture to his right wrist and several foreign body injuries in an arm, Dortmund spokesperson Sasche Fligge said.

The match was postponed and rescheduled for today, ahead of two other ties including fellow German side Bayern Munich against holders Real Madrid.

The nature of the explosive devices was not immediately known, however it is believed they could have been placed in a hedge near the hotel car park.

The incident occurred around 7.15pm local time (1.15am today in Malaysia) in the Hoechsten district, around 10 kilometres from the club’s stadium, as the Dortmund squad left the team hotel for the stadium.

After it was announced the match was being postponed, spectators already inside the ground left without incident. Police said there were three separate explosions, bursting one of the vehicle's windows.

Dortmund's Swiss goalkeeper Roman Buerki told the Swiss newspaper Blick: "I was sitting in the back row next to Marc Bartra who was hit by shards from the burst back window.

"The bus had turned onto the main road when there was a big bang - a real explosion."

Widespread condemnation of attack

Police deployed a drone to search for other possible explosive devices in the area around the team hotel. Lange said a suspicious object was found which had the appearance of an explosive device but was not capable of being detonated.

Dortmund chief executive Hans-Joachim Watzke told Germany's Sky television there was an "explosive attack in the immediate vicinity of the hotel exit" as the bus moved from the hotel car park into Wittbraeucker Strasse.

"The team and the coaching staff are of course shocked. We must now channel it in some way," he said.

"It will not be easy to get that out of the mind. In such a crisis situation, all at Borussia pull together. I think the team will feel it tomorrow."

Club president Reinhard Rauball said: "Of course this is an extremely difficult situation for the players. But they are professionals, and I am convinced that they will put that away and will give a performance tomorrow."

Football's world governing body Fifa and European football body UEFA condemned the attacks. UEFA president Aleksander Ceferin said both clubs had reacted well to the incident.

"The decision to postpone the Champions League match between Borussia Dortmund and AS Monaco was the right one," he said.

German government spokesperson Steffen Seibert in a Twitter message wished Bartra a speedy recovery and praised Monaco fans in the stadium for chanting support for Dortmund after hearing news of the blasts.

"Great reaction of the Monaco fans. This evening we are all behind @BVB," he tweeted in German.

Interior Minister Thomas de Maiziere said via his ministry's Twitter account: "My thoughts are with the team. Now we need to clarify the background."

International Olympic Committee president Thomas Bach also tweeted in support for Borussia.

Dortmund's Ruhr region rivals Schalke from nearby Gelsenkirchen wished Bartra a speedy recovery and Dortmund fans a safe journey home.

"In moments like these the region holds closely together," the club tweeted. Several other Bundesliga clubs, including Bayern Munich, sent similar messages of support.

Among international solidarity, English Premier League side Liverpool, managed by former Borussia coach Juergen Klopp, tweeted: "Thinking about all of our friends at @BVB this evening. YNWA ("You''ll Never Walk Alone").

- dpa