Microsoft has said that Yahoo Japan's decision to replace its Bing service with Google, as its main search partner, was anticompetitive.
In a statement sent to reporters, Microsoft's general counsel Brad Smith said the agreement is even more anticompetitive than Google's deal with Yahoo in the US and Canada, which the Department of Justice had termed as illegal.
The deal means there will be no search competition in Japan and that Google will end up controlling all personal search information for Japanese consumers and businesses, Microsoft said.
Microsoft did not say whether it would challenge the deal on legal grounds.
On Tuesday, Yahoo Japan announced that it had signed a deal with Google to provide search and related advertising services.
Some of the country's most popular websites are run by Yahoo, with almost nine out of ten Internet users in the country visiting them, according to comScore.
