The United States and Google Inc separately said they would move against Chinese Internet censorship, possibly signaling the start of a harder line toward China by U.S. President Barack Obama and the end of Google's business in the country.

Secretary of State Hillary Clinton plans to help citizens in other countries, including China, get uncensored access to the Internet, and last week she met top executives from companies including Google, Microsoft Corp, Twitter and Cisco Systems Inc, an aide said on Tuesday.

Google separately said it might pull out of China, closing down its Chinese-language Web site and shutting its offices, because of censorship and a series of China-based cyber attacks on human rights activists using its Gmail service around the world.

Relationships between the world's two biggest economies have been strained recently over climate change, trade and other matters. China also is the largest lender to the United States, holding around $800 billion in Treasury bills.

It was not clear if the U.S. search company, which described China as immaterial to its finances, and the United States government coordinated their moves.

U.S. State Department spokesman P.J. Crowley, responding to the Google move, said every nation should criminalize malicious activities on computer networks.

I defer to Google for details of its decision. Google was in contact with us prior to the announcement. Every nation has an obligation, regardless of the origin of malicious cyber activities, to keep its part of the network secure. That includes China, Crowley said.

Some 20 other companies also were attacked by unknown assailants based in China, said Google. It said, when asked, that it did not specifically know if the Chinese government was behind the attacks and was investigating.

China has the largest number of Internet users in the world and its policy of filtering and restricting access to Web sites has been a frequent source of tension with the United States and tech companies like Google and Yahoo Inc.

Clinton will unveil the tech policy initiative on Internet freedom on January 21, aide Alec Ross said in an interview with Reuters.

If you think about Internet freedom from the Caucasus to China to Iran to Cuba and elsewhere, people do not have universal access to an uncensored Internet, Ross said.

Our policies on Internet freedom in part are a response to the fact there are countries around the world that systematically stifle their citizens' access to information.

Google said it was working with the U.S. government over the security breaches. Google Chief Executive Eric Schmidt was a major campaign backer of President Barack Obama, and Schmidt was one of the executives meeting with Clinton.

China recently accused Google of allowing the spread of pornography on its search engine, which is second to local search provider Baidu Inc in that market.

(Writing by Peter Henderson in San Francisco; Editing by Steve Orlofsky)