Microsoft Corp was off to a good start with its revamped search engine Bing that was launched a few weeks earlier, Chief Executive Officer Steve Ballmer said on Wednesday.

Bing, which had its full launch on June 3, is up against Internet search leaders Google Inc and Yahoo Inc.

We have had some very good initial response, Ballmer said at a conference in Detroit.

Microsoft's Bing has lots of ground to make up. In April, the last full month for which figures are available, Microsoft's sites took 8.2 percent of U.S. Internet searches, trailing Yahoo with 20.4 percent and Google with 64.2 percent.

Acknowledging the tough task of beating strong rivals like Google, who he referred to as a big dog competitor, Ballmer said he did not want to set expectations too high.

I don't want to over set expectations, he said. We are going to have to be tenacious and keep up the pace of innovation over a long period of time.

When you are sitting there as we are in the search base, you got a 8 percent share and there's kind of a ... big dog competitor out there in the marketplace, you can do very interesting things, he added.

The world's largest software company has long been determined to play a major role in the lucrative Web search market after watching upstart Google take a stranglehold.

Both Google and Yahoo have recently introduced new features in their search engines to attract users, making Microsoft's task even harder.

Industry tracker comScore Inc said earlier on Wednesday Microsoft's share of search result pages in the United States rose to 12.1 percent for the period of June 8-12, up from 11.3 percent in the June 1-5 period, and up from 9.1 percent in the work week prior to Bing's introduction.

(Reporting by Poornima Gupta; Editing Bernard Orr)