In a posting on Twitter, she wondered how long Cuban Internet users would be able to view her Generation Y blog, (www.desdecuba.com/generaciony/), but exulted in the opening, however brief.

"In the long night of censorship, a small hole has opened. My blog Generation Y returns to the insular light," the 35-year-old blogger said.

Her blog, which criticizes the Cuban system and the difficulties of daily life on the communist-led island, is little known in Cuba, where Internet access is limited, but she has an international audience.

Sanchez has become the new face of political opposition in Cuba, replacing an old guard less conversant in new technologies, and she has earned the enmity of the Cuban government, which frequently criticizes her on its websites.

She was mentioned prominently last week in a leaked videotape of a government meeting about the Internet as the new battlefield in Cuba's ongoing ideological conflict with the United States.

Sanchez has won a number of international prizes and was named one of the 100 most influential people in the world by Time Magazine in 2008.

Her blog is translated into 15 languages and she has more than 100,000 followers on Twitter.

A Cuban government official did not respond to questions about why Sanchez's blog has been unblocked, but it came as Cuba hosted an international computer science conference.

(Reporting by Nelson Acosta and Esteban Israel; Editing by Jeff Franks and Paul Simao)