FRANKFURT, Feb 16 (Reuters) - Deutsche Boerse DB1Gn.DE Chief Executive Carsten Kengeter said a failure to complete a merger with the London Stock Exchange LSE.L would weaken Germany's main financial centre, Frankfurt, which has become less competitive in recent years.

"Any concerns that Frankfurt as a financial centre might be disadvantaged by the proposed business combination fail to recognise one thing: the biggest risk to Frankfurt... is doing nothing," Kengeter said at a news conference to discuss Deutsche Boerse's annual financial results.

"We are prepared to do something to make Frankfurt flourish. But we all have to recognise that in a 10-year comparison of financial centres worldwide according to the Global Financial Centres Index, Frankfurt has slipped from sixth place to number 19," Kengeter said. "To this end, we will need the boost that the merger with London would bring."

Deutsche Boerse will create an additional 300 jobs in Frankfurt, Kengeter said, adding that he was engaged in constructive talks with policymakers in Hesse, the German state where Deutsche Boerse is headquartered and with antitrust regulators in Brussels.

"We are engaged in a constructive dialogue. Through our referendum committee, we are going to ensure that the combined group will meet all regulatory requirements with regard to closing the transaction," Kengeter said.

Kengeter further said insider trading allegations against him would prove unfounded, given he had no role in determining the timing of his share purchases ahead of the announcement of merger plans with the London Stock Exchange LSE.L .

"We, Deutsche Boerse and myself, are fully cooperating with the public prosecutor. I am certain that, following detailed investigation, the allegations will turn out to be unfounded," Kengeter said at a news conference to discuss the exchange operator's annual results.

"When I purchased the shares using my own funds, I did not do so at a time of my own choosing. I did so between 1 and 21 December 2015 within a time-frame fixed by the Supervisory board," Kengeter said, adding that the shares were subject to a holding period until the end of 2019.

(Reporting by Edward Taylor; Editing by Maria Sheahan) ((Edward.Taylor@thomsonreuters.com; +49 69 7565 1187))