MEXICO CITY—Cuba's best-known blogger was arrested Thursday to keep her from covering a sensitive criminal trial involving the death of a famous dissident. But then the world noticed.

News agencies blogged about the details of the arrest. Human rights groups condemned it. By late Friday, the blogger, Yoani Sanchez, was released.

So it goes in the Caribbean nation headed by Fidel Castro's younger brother, Raul, whose government has released dozens of long-term political dissidents in the last few years—but also has detained government critics and troublemakers for brief periods in an apparent effort to thwart negative news coverage and stifle public criticism.

The detention of Sanchez, who said she was held for about 30 hours, became a telling footnote in the case of Angel Carromero, a conservative Spanish politician who is accused of causing the death of a Cuban dissident in a car crash this summer.

Sanchez was arrested along with her husband and fellow blogger, Reinaldo Escobar, and a number of other antigovernment figures in the city of Bayamo, about 400 miles east of Havana.

Sanchez had traveled to Bayamo to cover the Carromero's trial, which began Friday.

Carromero, a member of Spain's conservative Popular Party, crashed his rental car in the Bayamo area while visiting the island July 22. Cuban officials have accused him of speeding and causing the deaths of dissident Oswaldo Paya and another Cuban activist, who were riding in the car. Carromero faces up to 10 years in prison.

Early Friday, the pro-government blog www.yohandry.com asserted that Sanchez had traveled to Bayamo “to start a provocation and a media show to harm the proper conduct of the trial.”

News of her arrest quickly spread across the Internet. In addition to her acclaimed “Generation Y” blog, Sanchez's work has appeared regularly in the influential Spanish newspaper El Pais, among other international publications. The Cuban government's wary tolerance of her writing has in itself become a measure of its current stance on free-speech rights.

The arrests also sparked immediate condemnation from groups such as the Committee to Protect Journalists.

“The arrest of these journalists clearly indicates that the Cuban government continues its practice of punishing independent reporting,” Carlos Lauria, the Americas senior program coordinator at the Committee to Protect Journalists, said in a statement Friday. “Cuban authorities must immediately and unconditionally release Sanchez … and allow all Cuban reporters to report without fear of intimidation.”

By Friday evening, Sanchez, whose voice had disappeared from Twitter during her detention, was back on the social network with a message: “We have been freed! Thank you to all of those who raised their voices and their tweets, and allowed us to go home.”

It was not clear from her Twitter messages how many others among those arrested had been released. About half a dozen antigovernment activists had been rounded up along with Sanchez and Escobar before the trial, according to the independent Cuban Commission for Human Rights and National Reconciliation.

But Sanchez said that at least one other blogger, Henry Constantin, remained in government custody as of Friday evening.

Raul Castro, who took the reins of government from brother Fidel in 2006, has been tinkering with social and market reforms in the communist nation while simultaneously maintaining a level of control over the Cuban people and economy.