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German prosecutors are investigating Deutsche Boerse boss Carsten Kengeter over possible insider trading.

Mr Kengeter bought around 4.5m euros (£3.85m) of stock in his own company just over two months before the German exchange announced merger talks with the London Stock Exchange.

Deutsche Boerse said the December 2015 purchase was related to its remuneration programme.

"The accusations are groundless," Deutsche Boerse's Joachim Faber said.

"Only in the second half of January 2016 did the two chairmen and CEOs agree to begin negotiations for a merger of LSE Group and Deutsche Boerse," the Deutsche Boerse supervisory board chairman added.

The company and the chief executive were fully cooperating with the Frankfurt public prosecutor's office, it said.

Mr Faber, who is chairman of Deutsche Boerse's board, said Mr Kengeter bought the shares before an end-of-December deadline set by the group's management remuneration programme.

Under the programme, he could make a one-off share purchase worth up to 4.5m euros, which he would need to keep until the end of 2019.

As part of the deal, he received "co-performance shares" to the same amount, whose value depends on Deutsche Boerse's profits and its share price movement relative to a benchmark index.

Deutsche Boerse's stock has gained around 11% since Mr Kengeter bought the shares.

The European Commission is investigating the planned merger.