Twitter is to start selectively blocking tweets on a country by country basis, marking a dramatic turnaround in the firm's policy after it played a pivotal role in uprisings in the Middle East last year. In a blog post, Twitter says it will censor tweets in countries that have "different ideas" about freedom of expression in order to ensure it can continue operating in those markets as the firm continues its international expansion. The firm says it will only screen individual tweets in certain countries "when required to", while keeping the message available in the rest of the world. Although the firm says it has not yet used this power, and will alert the user if a tweet is blocked, the move is likely to be met with dismay from human rights groups in countries, such as China, with heavy internet censorship.

"As we continue to grow internationally, we will enter countries that have different ideas about the contours of freedom of expression," says Twitter in a blog post. However, the firm concedes that even these concessions will not be sufficient to penetrate regions with the most restrictive governments: "Some differ so much from our ideas that we will not be able to exist there."

Twitter cites cultural and historically sensitive material such as pro-Nazi tweets, illegal in countries including France and Germany, as the type of content that will fall into this category. Twitter says it has, until now, been forced to remove content globally, if it does so at all, but gives no indication of the number of tweets it removes at the request of government authorities. The micro-blogging service is emphasising the "transparency" of the censoring process, no doubt aware that the move will pitch it into a maelstrom of accusations over the right to free speech on the internet.

Finding itself at the centre of civil unrest in the Middle East last year, the firm was hailed by civil liberties groups for taking a solid hands free approach, writing in a blog post at the time that its position on the freedom of expression "carries with it the mandate to protect our users' rights to speak freely". The move to censor content is also at odds with general counsel Alex Macgillivray's comments last year that the firm was "from the free speech wing of the free speech party".

Twitter is, however, not the first internet firm to face difficulties expanding into certain regions, with both Google and Facebook coming up against free speech and privacy issues in countries such as China. Google walked out of the country in 2010, relocating its search engine to Hong Kong after a drawn-out dispute over privacy and allegations that the government had hacked into the internet firm's servers. Meanwhile, Facebook CEO Mark Zuckerberg is known to have met with Chinese government officials last year and is, like the majority of Western tech firms, keen to tap the region's enormous online population.

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