Twitter has refined its technology so it can censor messages on a country-by-country basis.

The additional flexibility is likely to raise fears that Twitter's commitment to free speech may be weakening. It comes as the short-messaging company expands into new countries in an attempt to broaden its audience and make more money.

But Twitter sees the censorship tool as a way to ensure individual messages, or "tweets," remain available to as many people as possible while it navigates a maze of different laws around the world.

Before, when Twitter erased a tweet it disappeared throughout the world. Now, a tweets containing content breaking a law in one country can be taken down there and still be seen elsewhere.

Twitter will post a censorship notice whenever a tweet is removed.