MILAN/LONDON, Sept 14 (Reuters) - Swiss stock exchange operator Six has made the highest offer for Borsa Italiana and is ahead of France's Euronext and Germany's Deutsche Boerse in the takeover battle for the Milan bourse, two sources familiar with the matter said.

The three bids value Borsa Italiana at 3.5 billion euros to 4 billion euros ($4.15-$4.74 billion), one of the sources said.

The London Stock Exchange (LSE), which took control of Borsa in 2007 for 1.6 billion euros, is now trying to sell it as part of the regulatory remedies to clear its $27 billion acquisition of data provider Refinitiv.

Six became Europe's third-largest stock exchange operator by revenue after completing a 2.57 billion euro takeover of Spanish rival BME earlier this year.

Six and the other bidders declined to comment. ($1 = 0.8433 euros) (Reporting by Elvira Pollina in Milan and Pamela Barbaglia in London, editing by Louise Heavens)