Four Cuban dissidents who distributed leaflets branding the Castro brothers as “assassins” were sentenced to up to five years in prison Tuesday — bringing the number of government critics convicted this year to eight, compared to two in all of 2010.

The convictions represent a significant shift for the Raúl Castro government, which seemed to prefer detaining dissidents for a few hours to threaten them, rather than throwing them in jails for years, said Havana human rights activist Elizardo Sánchez.

“It’s evident that there’s a change, let’s say in the character of the political repression,” Sánchez added. “Suddenly, there’s been a shift toward the trials and sentences” more often seen under brother Fidel Castro’s rule.

Raúl Castro may well be using the convictions to warn Cubans to watch their step at a time when he’s trying to adopt some risky economic reforms, including a shift away from socialism and toward market forces, he added.

The four men who distributed the leaflets were tried and sentenced in about three hours Tuesday — five years for Luis Enrique Labrador, 33, David Piloto, 40, and Walfrido Rodriguez, 42, and three years for Yordani Martinez, 23.

Police arrested them after they spread leaflets with two messages, “The Castros are assassins” and “Down with the Castros’ tyranny” in mid-January on Havana’s famed corner, La Esquina de Tejas.

Sanchez said prosecutors charged them with disturbing the peace and “contempt for authority” — apparently because the corner is near the main government building, the Palace of the Revolution, where Castro has some of his offices.

“They are absolutely innocent because they acted within the limits of freedom of expression that exists in almost any other country,” he told El Nuevo Herald by phone from Havana, adding that they should be considered as political prisoners.”

A government-organized mob harassed relatives and supporters of the four after the trial in Havana’s La Vibora district. Police also arrested at least a dozen supporters who protested outside the courthouse after the verdict was handed down, Sánchez added.

Tuesday’s conviction came a week after two young brothers, Antonio Michel and Marcos Maikel Lima, were sentenced to two and three years in prison, respectively, for “public disorder” and “disrespecting patriotic symbols” for using rap lyrics critical of the government.

The brothers were arrested Dec. 25 after they allegedly either sang or played the music to a mob of government supporters that was harassing their home in the eastern city of Holguín. The music was by Los Aldeanos, a duo that often attacks the communist system.