BERLIN- Germany's national railway operator, Deutsche Bahn, must fetch the book value of its international transit subsidiary Arriva in the event of an initial public offering of the unit, sources familiar with the situation told Reuters on Wednesday.

The sources said there were still questions - that could affect a listing - concerning investments in Arriva, which operates the London Overground rail system, as well as on the effect of Britain's planned exit from the European Union.

Deutsche Bahn's supervisory board will not decide on the details of the planned IPO at its December meeting, the company and supervisory sources added.

The CEO of the state-owned group earlier said Deutsche Bahn aims for an initial public offering (IPO) of Arriva next year. 

(Reporting by Markus Wacket; writing by Thomas Seythal; editing by Paul Carrel) ((berlin.newsroom (at) thomsonreuters.com; +49 30 2888 5156;))