Yahoo Japan on Tuesday announced that is has signed a deal to use Google for its search engine and search ad delivery system. Microsoft quickly criticized the deal.

Yahoo Japan on Tuesday announced that is has signed a deal to use Google for its search engine and search ad delivery system.

Yahoo Japan will continue to manage its own search page and search service. Yahoo Japan will also continue to run its advertising marketplace independent of Google.

Microsoft condemned the deal and said it would result in Google gaining nearly complete control over search and search advertising in Japan through contract, not organic growth.

Yahoo Japan denied this. "Yahoo Japan and Google will continue to compete with each other in all service areas including their advertising and search services," the company said in a statement.

Yahoo Japan said the value of its search service "will stay at a high level" if it uses Google's services. Improved search will also increase the value of other Yahoo Japan services, the company said.

Yahoo Japan and Google have not yet determined a timeline for when the deal will be put into place.

Yahoo Japan is jointly owned by Yahoo and Softbank. Yahoo Japan said the Google deal "will have no change" on other business areas, "including Yahoo's equity ownership in Yahoo Japan."

The announcement comes one year after Yahoo under which Microsoft will power Yahoo's search site while Yahoo will manage the sales force for both companies' premium search advertisers.

Referencing the Yahoo-Microsoft deal, Yahoo Japan said it examined several search engines and ad platform technologies, but ultimately decided that "Google has developed what we believe is the best-performing search engine and ads platform technology for the Japanese language environment."

Microsoft made an unsolicited bid for Yahoo in February 2008, but after much back and forth, a bid for Yahoo's search business, and a proxy bid for Yahoo by billionaire investor Carl Icahn, a combined Microsoft-Yahoo never came to fruition.

Google with Yahoo that would have allowed the Internet company access to Google's AdSense for search and content advertising programs in the U.S. and Canada. Regulatory scrutiny, however, later .

Dave Heiner, vice president and deputy general counsel at Microsoft, said Tuesday that the Yahoo Japan-Google deal is "even worse" than the failed Google-Yahoo 2008 deal.

"Today Google accounts for about 51 percent of paid search advertising in Japan. Yahoo Japan accounts for 47 percent. Their combined share of natural search results is almost as high," Heiner wrote in a blog post. "If Google is permitted to proceed with its plan, it would gain nearly complete control over search and search advertising in Japan through contract, not organic growth. Google alone would decide what consumers in Japan will find, or not find, on the Web. And Google will obtain massive amounts of data regarding the search history and Web sites visited by every consumer, business and government agency that conducts Web searches."

Heiner said the attempted Google-Yahoo match-up "was not nearly so far-reaching."

"Less than two years later Google has entered into a deal that would turn its only major competitor in Japan into a collaborator, rather than a competitor, across natural search results and advertising," Heiner concluded. "In doing so, Google has engineered a transaction that, once again, would deprive its search rivals of needed search query scale."

Google said its deal with Yahoo Japan is different from its proposed deal with Yahoo in 2008.

"Google will only be licensing its advertising platform services to [Yahoo Japan], and will not be providing its ads to appear on YJC," Google said in a statement. "YJC will continue to manage their own advertising system and advertiser relationships, and both companies' advertisers and advertising data will remain entirely separate."

Yahoo Japan will be able to customize how its users see Google's search services, and "users should continue to expect very different experiences" on Yahoo Japan than they might see on Google. The company insisted the deal is "commonplace in the business world, and it doesn't foreclose any robust competition." The Japan Fair Trade Commission has no objection to the deal, Google said.

"Competition between Google and YJC, as well as others in the online advertising market, will remain vigorous because their advertising operations will stay independent of one another, and there is competition with other online advertising service providers," the company concluded.

Editor's Note: This story was updated Wednesday with comment from Google.