Twitter, a tool of choice for dissidents and activists around the world, found itself the target of global outrage Friday after unveiling plans to allow country-specific censorship of tweets that might break local laws.

It was a stunning role reversal for a youthful company that prides itself in promoting unfettered expression, 140 characters at a time. Twitter insisted its commitment to free speech remains firm, and sought to explain the nuances of its policy, while critics _ in a barrage of tweets _ proposed a Twitter boycott and demanded that the censorship initiative be scrapped.

"This is very bad news," tweeted Egyptian activist Mahmoud Salem, who operates under the name Sandmonkey. Later, he wrote, "Is it safe to say that (hash)Twitter is selling us out?"

In China, where activists have embraced Twitter even though it's blocked inside the country, artist and activist Ai Weiwei tweeted in response to the news: "If Twitter censors, I'll stop tweeting."

One often-relayed tweet bore the headline of a Forbes magazine technology blog item: "Twitter Commits Social Suicide"

San Francisco-based Twitter, founded in 2006, depicted the new system as a step forward. Previously, when Twitter erased a tweet, it vanished throughout the world. Under the new policy, a tweet breaking a law in one country can be taken down there and still be seen elsewhere.

Twitter said it will post a censorship notice whenever a tweet is removed and will post the removal requests it receives from governments, companies and individuals at the website chillingeffects.org.

The critics are jumping to the wrong conclusions, said Alexander Macgilliviray, Twitter's general counsel.

"This is a good thing for freedom of expression, transparency and accountability," he said. "This launch is about us keeping content up whenever we can and to be extremely transparent with the world when we don't. I would hope people realize our philosophy hasn't changed."

Some defenders of Internet free expression came to Twitter's defense.

"Twitter is being pilloried for being honest about something that all Internet platforms have to wrestle with," said Cindy Cohn, legal director of the Electronic Frontier Foundation. "As long as this censorship happens in a secret way, we're all losers."

State Department spokeswoman Victoria Nuland credited Twitter with being upfront about the potential for censorship and said some other companies are not as forthright.

As for whether the new policy would be harmful, Nuland said that wouldn't be known until after it's implemented.

Reporters Without Borders, which advocates globally for press freedom, sent a letter to Twitter's executive chairman, Jack Dorsey, urging that the censorship policy be ditched immediately.

"By finally choosing to align itself with the censors, Twitter is depriving cyberdissidents in repressive countries of a crucial tool for information and organization," the letter said. "Twitter's position that freedom of expression is interpreted differently from country to country is unacceptable."

Reporters Without Borders noted that Twitter was earning praise from free-speech advocates a year ago for enabling Egyptian dissidents to continue tweeting after the Internet was disconnected.

"We are very disappointed by this U-turn now," it said.

Twitter said it has no plans to remove tweets unless it receives a request from government officials, companies or another outside party that believes the message is illegal. No message will be removed until an internal review determines there is a legal problem, according to Macgilliviray.

"It's a thing of last resort," he said. "The first thing we do is we try to make sure content doesn't get withheld anywhere. But if we feel like we have to withhold it, then we are transparent and we will withhold it narrowly."

Macgilliviray said the new policy has nothing to do with a recent $300 million investment by Saudi billionaire Prince Alwaleed bin Talal Mac or any other financial contribution.

In its brief existence, Twitter has established itself as one of the world's most powerful megaphones. Streams of tweets have played pivotal roles in political protests throughout the world, including the Occupy Wall Street movement in the United States and the Arab Spring uprisings in Egypt, Bahrain, Tunisia and Syria.

Indeed, many of the tweets calling for a boycott of Twitter on Saturday _ using the hashtag (hash)TwitterBlackout _ came from the Middle East.

"This decision is really worrying," said Larbi Hilali, a pro-democracy blogger and tweeter from Morocco. "If it is applied, there will be a Twitter for democratic countries and a Twitter for the others."

In Cuba, opposition blogger Yoani Sanchez said she would protest Saturday with a one-day personal boycott of Twitter.

"Twitter will remove messages at the request of governments," she tweeted. "It is we citizens who will end up losing with these new rules ... ."

In the wake of the announcement, cyberspace was abuzz with suggestions for how any future country-specific censorship could be circumvented. Some Twitter users said this could be done by employing tips from Twitter's own help center to alter one's "Country" setting. Other Twitter users were skeptical that this would work.

While Twitter has embraced its role as a catalyst for free speech, it also wants to expand its audience from about 100 million active users now to more than 1 billion. Doing so may require it to engage with more governments and possibly to face more pressure to censor tweets; if it defies a law in a country where it has employees, those people could be arrested.

Theoretically, such arrests could occur even in democracies _ for example, if a tweet violated Britain's strict libel laws or the prohibitions in France and Germany against certain pro-Nazi expressions.

"It's a tough problem that a company faces once they branch out beyond one set of offices in California into that big bad world out there," said Rebecca MacKinnon of Global Voices Online, an international network of bloggers and citizen journalists. "We'll have to see how it plays out _ how it is and isn't used."

MacKinnon said some other major social networks already employ geo-filtering along the lines of Twitter's new policy _ blocking content in a specific jurisdiction for legal reasons while making it available elsewhere.

Many of the critics assailing the new policy suggested that it was devised as part of a long-term plan for Twitter to enter China, where its service is currently blocked.

China's Communist Party remains highly sensitive to any organized challenge to its rule and responded sharply to the Arab Spring, cracking down last year after calls for a "Jasmine Revolution" in China. Many Chinese nonetheless find ways around the so-called Great Firewall that has blocked social networking sites such as Facebook.

Google for several years agreed to censor its search results in China to gain better access to the country's vast population, but stopped that practice two years after engaging in a high-profile showdown with Chain's government. Google now routes its Chinese search results through Hong Kong, where the censorship rules are less restrictive.

Google Executive Chairman Eric Schmidt declined to comment on Twitter's action and instead limited his comments to his own company.

"I can assure you we will apply our universally tough principles against censorship on all Google products," he told reporters in Davos, Switzerland.

Google's chief legal officer, David Drummond, said it was a matter of trying to adhere to different local laws.

"I think what they (Twitter officials) are wrestling with is what all of us wrestle with _ and everyone wants to focus on China, but it is actually a global issue _ which is laws in these different countries vary," Drummond said.

"Americans tend to think copyright is a real bad problem, so we have to regulate that on the Internet. In France and Germany, they care about Nazis' issues and so forth," he added. "In China, there are other issues that we call censorship. And so how you respect all the laws or follow all the laws to the extent you think they should be followed while still allowing people to get the content elsewhere?"

Craig Newman, a New York lawyer and former journalist who has advised Internet companies on censorship issues, said Twitter's new policy and the subsequent backlash are both understandable, given the difficult ethical issues at stake.

On one hand, he said, Twitter could put its employees in peril if it was deemed to be breaking local laws.

"On the other hand, Twitter has become this huge social force and people view it as some sort of digital town square, where people can say whatever they want," he said. "Twitter could have taken a stand and refused to enter any countries with the most restrictive laws against free speech."

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Associated Press writers Paul Schemm in Rabat, Morocco; Michael Liedtke in San Francisco; Peter Orsi in Havana, Cuba; Cara Anna in New York and Ben Hubbard in Cairo contributed to this report.