Kazuyuki Furuya, chairman of Japan's Fair Trade Commission (FTC), also said Tokyo could open a probe into any merger or business tie-up involving fitness tracker maker Fitbit if the size of such deals are big enough.

"If the size of any merger or business-tie up is big, we can launch an anti-monopoly investigation into the buyer's process of acquiring a start-up (like Fitbit)," he told Reuters. "We're closely watching developments including in Europe."

EU antitrust regulators in August launched an investigation into a $2.1 billion deal by Alphabet unit Google's bid to buy Fitbit that aimed to take on Apple and Samsung in the wearable technology market.

Japan is laying the groundwork to regulate platform operators. Among them are big tech giants dubbed "GAFA" - Google, Apple, Amazon and Facebook - that face various antitrust probes in western nations.

Multi-national companies like GAFA have similar business practices across the globe, which makes global coordination crucial, Furuya said.

"We'll work closely with our U.S. and European counterparts, and respond if to any moves that hamper competition," he said.

"This is an area I will push through aggressively," he said, adding the FTC was ready to open probes if digital platformers abuse their dominant market positions against consumers.

Furuya, who assumed the post in September, also said the FTC would conduct research into Japan's mobile phone market to see whether there is any room for improvement to spur competition.

Any such move would help Prime Minister Yoshihide Suga's push to slash Japan's mobile phone charges, which he has repeatedly criticised as too high.

Furuya countered the view that helping the government meet its policy priorities could undermine the FTC's position as a body mandated to act independently from political meddling.

"If there's a policy priority for the government, there's no doubt the FTC should think about what it can do on that front," Furuya said.

"By participating in the government's debate on policy issues, we have been reflecting our thinking in the process. This is something our organisation should do."

(Reporting by Leika Kihara and Takahiko Wada; Editing by Chang-Ran Kim and Gerry Doyle)

By Leika Kihara and Takahiko Wada