(AP) -- The U.S. government has formally asked China to turn over details of its policies for censoring websites.

U.S. Trade Representative Ron Kirk said Wednesday in a statement that the request is being pursued under World Trade Organization rules governing how member countries deal with trade issues. Kirk said the concerns center on the competitiveness of foreign websites in China.

China heavily censors its Internet, and Kirk said the U.S. wants to understand China's rules governing website blocking so that foreign websites can adopt policies to avoid being blocked.

The request also seeks information on the mechanics of Internet censorship in China, and whether it's implemented directly by the government or indirectly by Internet providers.

Some 500 million people in China use the Internet. They are hotly pursued by marketers.

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