Twitter has announced that it would begin restricting Tweets in certain countries, marking a policy shift for the social media platform that helped propel the popular uprisings recently sweeping across the Middle East. It said even with the possibility of such restrictions, Twitter would not be able to coexist with some countries. Twitter gave as examples of restrictions it might cooperate with "certain types of content, such as France or Germany, which ban pro-Nazi content.

"As we continue to grow internationally, we will enter countries that have different ideas about the contours of freedom of expression. Some differ so much from our ideas that we will not be able to exist there," Twitter wrote in a blog post published Thursday. In the interest of transparency, Twitter said Thursday, it has built a mechanism to inform users in the event that a Tweet is being blocked.

Twitter's move comes at a time when internet companies such as Google and Facebook have wrestled with foreign governments over freedom of speech and privacy issues as they expand rapidly overseas.