China hit back hard against U.S. criticism of Beijing's controls over the Internet, saying on Friday that Washington's push against online censorship could harm relations between the two big powers.

U.S. Secretary of State Hillary Clinton's speech against Internet censorship on Thursday raised contention with Beijing over cyber policy, which flared after Google Inc last week warned it could pull out of China over hacking and restrictions.

Chinese Foreign Ministry spokesman Ma Zhaoxu said the U.S. criticisms could hurt ties between the two nations -- the world's biggest and third biggest economies -- already frayed over trade imbalances, currency values and U.S. weapons sales to Taiwan.

The U.S. has criticized China's policies to administer the Internet and insinuated that China restricts Internet freedom, said Ma, in a statement carried on the Foreign Ministry website www.mfa.gov.cn.

This runs contrary to the facts and is harmful to China-U.S. relations.

We urge the United States to respect the facts and cease using so-called Internet freedom to make groundless accusations against China, Ma said without mentioning Clinton by name.

But the spokesman also indicated that his government did not want to see the dispute overwhelm cooperation with the Obama administration, which has sought Beijing's backing on economic policy and diplomatic standoffs, such as Iran and North Korea.

Ma said each side should appropriately handle rifts and sensitive issues, protecting the healthy and stable development of China-U.S. relations.

Clinton's speech criticized the cyber policies of China and Iran, among others, and demanded Beijing investigate complaints by Google Inc, the world's biggest search engine operator, about hacking and censorship.

A new information curtain is descending across much of the world, said Clinton, calling growing Internet curbs the present-day equivalent of the Berlin Wall that contravene international commitments to free expression.

Facebook, Twitter and YouTube are blocked in China, which uses a filtering firewall to prevent Internet users from seeing overseas web sites with content anathema to the Communist Party.

U.S. Assistant Secretary of State Kurt Campbell told reporters Washington had discussed the Google case with China several times from working levels to very senior levels.

It was unclear how the United States could prod China into opening up the Internet. Some fear strong-arm tactics could backfire and make China control content even more tightly.

TESTING TIMES

Ties between China and the United States have been put to the test in recent months over trade, currency, climate change and arms sales to Taiwan.

This month, China denounced the U.S. sale of Patriot air defense missiles, capable of intercepting Chinese missiles, to Taiwan, which Beijing claims as its own.

China announced its own anti-missile test soon after.

Beijing has warned that more U.S. weapons sales to Taiwan could badly bruise relations with Washington, and has urged President Barack Obama not to meet the Dalai Lama, the exiled Buddhist leader of Tibet who Beijing denounces as a separatist.

I think over the short haul (the Google issue) is going to go away because other problems that the U.S. and China face are rather numerous, said Niu Jun, an international studies expert at Peking University.

I think economic and trade issues are still more important. Both sides will find a positive solution through talks. But this is not necessarily just a simple commercial issue. I don't know what the solution will be. But it won't take a long time.

Among other issues, Beijing accuses Washington of protectionism in anti-dumping cases against Chinese exports like tires and steel, while Washington says Beijing stokes global economic imbalances and the U.S. trade deficit by undervaluing its currency. (Additional reporting by Lucy Hornby and Yu Le; Editing by Jeremy Laurence)

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