BRUSSELS, March 26 (Reuters) - The European Commission said on Tuesday it had dropped an investigation into a Chinese train maker's participation in a Bulgarian tender for electric trains after the company withdrew from the bidding.

Last month, EU antitrust regulators used tough new rules to open an investigation into whether subsidies to Chinese train maker CRRC Qingdao Sifang Locomotive might give it an unfair advantage in the tender.

It was the first investigation under the EU Foreign Subsidies Regulation that took effect in July to try to stop distortive subsidies.

The Commission said in a statement it took note of the withdrawal by CRRC Qingdao Sifang Locomotive from the Bulgarian tender following its announcement of an in-depth investigation under the Foreign Subsidies Regulation.

It added that as a result of the withdrawal, it will close the investigation.

"In just a few weeks, our first investigation under the Foreign Subsidies Regulation has already yielded results. Our Single Market is open for firms that are truly competitive and play fair," EU industry chief Thierry Breton said in a statement.

The tender - with an estimated value of 610 million euros ($661 million) - is for 20 electric "push-pull" trains and for their maintenance over 15 years.

($1 = 0.9234 euros) (Reporting by Foo Yun Chee; writing by GV De Clercq; editing by Jonathan Oatis and Chizu Nomiyama)