Until now, Twitter had to remove a Tweet from its global network if it received a takedown request from a government. But the company said in a blog post published Thursday that it now has the ability to selectively block a Tweet from appearing to users in one country.

"Starting today, we give ourselves the ability to reactively withhold content from users in a specific country while keeping it available in the rest of the world," the Twitter blog said.

Twitter gave as examples of restrictions it might cooperate with, such as "pro-Nazi content" in France and Germany, where it is banned.

It said even with the possibility of such restrictions, Twitter would not be able to coexist with some countries. "Some differ so much from our ideas that we will not be able to exist there," it said.

"As we continue to grow internationally, we will enter countries that have different ideas about the contours of freedom of expression," Twitter wrote.

In the interest of transparency, Twitter said, it has built a mechanism to inform users in the event that a Tweet is being blocked.

A Twitter spokeswoman declined to elaborate on the blog.

Twitter's acknowledgement that it will censor content represents a significant departure from its tone just one year ago, when anti-government protesters in Tunisia, Egypt and other Arab countries coordinated mass demonstrations on the social network and, in the process, thrust Twitter's disruptive potential into the global spotlight.

As the revolutions brewed last January, Twitter signaled that it would take a hands-off approach to censoring content in a blog post entitled "The Tweets Must Flow."

"We do not remove Tweets on the basis of their content," the blog post read. "Our position on freedom of expression carries with it a mandate to protect our users' right to speak freely and preserve their ability to contest having their private information revealed."

And last year, Twitter General Counsel Alex Macgillivray declared that the company was "from the free speech wing of the free speech party."

Still, some open Internet advocates said it appeared Twitter did the best it could to navigate the dueling responsibilities of complying with local law and upholding free speech.

Twitter would be banned outright in many countries if it did not agree to restrict Tweets, said Cynthia Wong of the Center for Technology & Democracy.

"The question is: What's best for freedom of speech?" Wong said. "If Twitter was completely blocked from certain countries, is that really better? It looks like Twitter has done a good job in thinking through how to mitigate the human rights harm in complying with local law."

Twitter's move highlighted the frequent tensions over freedom of speech and privacy issues between foreign governments and Internet companies such as Google and Facebook as they expand rapidly overseas.

In 2010 Google relocated its Web search engine to Hong Kong, following a very public spat with the Chinese government over its refusal to bow to Beijing's Web censorship requirements and a hacking episode that Google said it had traced to China.

(Reporting By Gerry Shih; Editing by Gary Hill)

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