Letter claiming responsibility for Dortmund attack is unusual - official

Football Soccer - Borussia Dortmund v AS Monaco - UEFA Champions League Quarter Final First Leg - Signal Iduna Park, Dortmund, Germany - 11/4/17 The Borussia Dortmund team bus is seen after an explosion near their hotel before the game. Reuters / Kai Pfaffenbach/File Photo

DUESSELDORF, Germany (Reuters) - The interior minister of the German state of North Rhine-Westphalia described as "unusual" a letter claiming responsibility for Tuesday's attack on a bus carrying players from soccer club Borussia Dortmund.

Ralf Jaeger told reporters that police in North Rhine-Westphalia had again taken additional security measures in Dortmund, where Borussia and AS Monaco will face off for their postponed Champions League clash on Wednesday evening.

(Reporting by Anneli Palmen; Writing by Paul Carrel; Editing by Joseph Nasr)