PHOENIX (AP) -- Arizona regulators have ordered a Seattle-based online home price estimator to stop doing business in the state.

The Arizona Board of Appraisal issued two cease-and-desist letters to the company that operates the popular real estate Web site Zillow, saying it needs an appraiser license to offer its "zestimates" in Arizona.

"It is the board's feeling that (Zillow) is providing an appraisal," Deborah Pearson, the board's executive director, said Friday.

Zillow warns users the estimates it provides are not a definitive value but a starting point for consumers. Launched in February, 2006, the company claims it has 4 million users a month, including people wanting to how much their homes - or their neighbors' homes - are worth.

The site has been criticized by real estate professionals and others concerned about its accuracy.

A complaint was filed in October with the Federal Trade Commission by the non-profit National Community Reinvestment Coalition, alleging Zillow was misleading consumers and others with its estimates.

Zillow issued a statement Saturday saying it disagreed with the board's view, and pointed to an opinion issued by a national appraisers standards group that said online estimates aren't formal appraisals.

"We strongly believe that providing Zestimates in Arizona is completely legal and in fact an important public service, given that Zestimates are the result of our 'automated valuation model' and are not a formal appraisal," co-founder and company President Lloyd Frink said in the statement.

Zillow's director of communications, Amy Bohutinsky, said the company has responded to the board's letters and hopes to "engage in a productive dialogue with them."

On Saturday, the Zillow.com Web site was still giving price estimates for homes in the Phoenix area.