June 6 (Reuters) - Antin Infrastructure Partners plans to launch a new high-speed train company in France called Proxima, the French private equity firm said on Thursday, adding it would initially invest 1 billion euros ($1.1 billion) in the project.

High-speed TGV train services in France had historically been a monopoly by state-owned giant SNCF, but Trentalia, a unit of Italy's state rail operator, entered the market in 2021.

Proxima will add to the competition, becoming the first privately-owned operator in this market in the country.

The new trains will connect Paris with four cities in western France - Bordeaux, Nantes, Rennes, and Angers - adding 10 million new passenger seats per year on routes which are showing strong demand, the company said in a statement.

"Travel between key cities in France has increased over the last 10 years, reflecting new ways of living. High-speed rail is the answer favored by the French, and train occupancy levels are at all-time highs," the company added.

Proxima has also entered into exclusive negotiations with French train maker Alstom to buy 12 of its flagship Avelia Horizon trains, with the option of buying more in the future.

($1 = 0.9194 euros) (Reporting by Olivier Sorgho and Leo Marchandon; editing by Jason Neely and Emelia Sithole-Matarise)