Japan's antitrust watchdog has begun a probe into Google on suspicion that the company is unfairly pressuring smartphone makers over permission for the use of its app store.

The Japan Fair Trade Commission said at a news conference on Monday that the US tech giant is suspected of violating the antimonopoly law.

The commission suspects Google has pressured smartphone manufacturers to load its search engine Google Chrome on their devices when permitting the use of its mobile app store called Google Play.

It said the tech firm allegedly requested the makers to set its search services as the default on their screens.

Google also reportedly distributed profits from advertisements linked to its search engine on condition that smartphone makers block rival search services.

The move by the Japanese watchdog comes after US and European authorities tightened regulations on big tech firms such as Google, Apple, Facebook and Amazon, known collectively as GAFA. The authorities say the firms are hindering free competition by monopolizing the market.

Japan's Fair Trade Commission says it will conduct its investigations to try to ensure fair and open competition. The move comes as competition in the tech market is entering a new phase with the rise of generative artificial intelligence, such as the emergence of dialogue search services.