Social media moved into a new realm in technologically backward Cuba Tuesday when Cuban President Raul Castro's controversial daughter Mariela began tweeting and quickly got into the Twitter equivalent of a shouting match with dissident blogger Yoani Sanchez.

Mariela Castro called Sanchez and her compatriots despicable parasites in a brief exchange that may have been the first direct confrontation, verbal or otherwise, between dissidents and a member of the Castro family after years of mutual animosity.

Sanchez, who regularly criticizes the lack of freedoms in communist Cuba in her internationally known Generation Y blog, touched off the dispute by sending tweets that welcomed Mariela Castro to the plurality of Twitter where no one can shut me up, deny me permission to travel or block entrance.

When will we Cubans be able to come out of other closets? she asked, alluding to Mariela Castro's championing of gay rights as head of Cuba's National Centre for Sex Education.

Tolerance is total or is it not? Sanchez tweeted.

Castro, 49, replied coolly with an obtuse putdown, saying, Your focus of tolerance reproduces the old mechanisms of power. To improve your 'services' you need to study.

But later, after apparently receiving a number of tweets from other dissidents, Castro lashed out.

Despicable parasites: did you receive the order from your employers to respond to me in unison and with the same predetermined script? Be creative, she wrote, reflecting the contempt Cuban leaders have for dissidents and the belief that they work for their longtime enemy the United States.

They can barely hide their rancour towards Sanchez in particular, but do not mention her or other dissidents by name. Despite having an international following, Sanchez is little known in Cuba where Internet access is limited.

Just as she is at the vanguard in Cuba in supporting gay rights, Mariela Castro appears to be the first in the Castro family to publicly and directly engage in tweeting.

Her father, who is 80, and her uncle, former leader Fidel Castro, 85, have Twitter accounts, but they are used only to post stories and columns from Cuba's state-run media.

After her exchange with Sanchez, she posted a link to an interview about her recent trip to Holland, where she toured Amsterdam's famous red-light district.

She raised eyebrows by saying there that she knew of Cubans who would prostitute themselves with labourers just so they could take a bath.

In a tweet, Mariela Castro said there had been manipulations, like always of her comments.

(Editing by Cynthia Osterman)