German authorities have opened a probe into stock buys made in 2015 by Deutsche Boerse group head Carsten Kengeter before the announcement of the market's planned merger with the London Stock Exchange, a spokesman said Wednesday.

The enquiry centres around a financial operation carried out by Kengeter on December 14, 2015, consisting of the purchase of shares worth about 4.5 million euros ($4.8 million) in the Deutsche Boerse group, the bourse spokesman told AFP.