Eric Schmidt, Google chief executive, told reporters at a news conference at the company's headquarters that Google did not need to receive government approval for the Yahoo! deal and would go ahead with it, as planned, next month.
He said: "The deal was designed precisely to meet the terms of antitrust laws in the United States because we knew people would raise these questions."
The partnership between and sees the two search engine giants combine their search advertising systems, which will allow Google to sell advertising on Yahoo! in return for a share of the profits.
But since the partnership was announced in June, it has come under intense scrutiny and both the US Department of Justice and the European Union Competition Commission are now reviewing the deal.
Schmidt went on to say that he believed rival Microsoft was behind plans to block the deal.
He said: "We are quite certain that Microsoft is busy helping everyone get upset about things.
"You face a question as a large company that is trying to change things: How many of these initiatives do you want to take on that are either unpopular or are going to lead to criticism? The guidance we use is - what's beneficial to the end user?"