Japan's Fair Trade Commission has been probing Google on suspicion that the major US IT company may have violated the antitrust law. 

Sources close to the situation said the antimonopoly watchdog suspects that Google placed unfair restrictions on its digital advertising distribution system provided to a fellow search engine operator. Google has provided the system to LY Corporation, which operates Yahoo Japan. 

The sources said that Google asked LYC to stop distributing smartphone ads to third-party portal sites. 

They said the commission notified the tech giant that the action may be in violation of Japan's antitrust law. 

In response, Google is believed to have voluntarily submitted an improvement plan that includes measures to prevent such action from happening again. 

The Fair Trade Commission is expected to issue an administrative action against Google after examining whether the content of the improvement plan will be implemented.