Updated at 6:00 p.m. ET

Three explosions went off near the bus of Germany's Borussia Dortmund soccer team on Tuesday evening in the city of Dortmund, local police say.

The team said on Twitter that one of its players, defender Marc Bartra, suffered a broken wrist and is being treated in a hospital. The injury required surgery.

Initial reports suggest that the blasts were caused by "serious explosives," potentially hidden in a bush near a parking lot, Dortmund police said in a statement.

Police and prosecutors have not identified who is behind the explosions.

Dortmund police chief Gregor Lange said late Tuesday that police assume the team bus was intentionally targeted, but that the origin of the attack was unclear, Reuters reports.

"I do not want to suggest that this was a terrorist attack," Lange said, according to Reuters. "All that is still being investigated."

A letter was found near the site of the explosion, and investigators are looking into its authenticity, police say. The Associated Press reports that the letter allegedly takes responsibility for the blasts.

The team was set to play against Monaco in the "Champions League quarterfinal first leg game," the AP reports. The explosions came "as the players were leaving their hotel for the match at 7 p.m. local time," the wire service writes.

Police said in a statement that the bus's windows were damaged.

"The match has been postponed until Wednesday," NPR's Lucian Kim reports from Berlin.

The Dortmund police added there is no indication the people in the stadium were in danger. They later praised fans for their orderly departure from the stadium after the match was cancelled.

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