An opposition political activist imprisoned since 2003 died on Tuesday after a lengthy hunger strike, members of Cuba’s human rights community said.

Orlando Zapata Tamayo, who was jailed on charges including disrespecting authority, died at a clinic at Havana’s Combinado del Este prison, according to Vladimiro Roca, a leading dissident who said he spoke to Zapata Tamayo’s family.

Zapata Tamayo, 42, was not among the island’s best—known dissidents. He was arrested in 2003 on charges of disrespecting authority, said Elizardo Sanchez, head of the Havana—based, independent Cuban Commission on Human Rights and National Reconciliation.

He was sentenced to three years in prison, which Mr. Sanchez said was lengthened to 25 years, in part because of his political activism while behind bars.

Mr. Sanchez said Zapata Tamayo staged a hunger-strike for weeks before his death. His family first announced last week that prison doctors said he was gravely ill.

Relatives were transporting Zapata Tamayo’s remains to his hometown in Holguin province, said Mr. Roca, a former fighter pilot and son of a legendary communist leader who served nearly five years in prison himself for his opposition political beliefs.

Word of Zapata Tamayo’s death was first reported on Cuban exile radio stations in southern Florida, which broadcast an interview with his mother, Reina Luisa Tamayo.

Rep. Lincoln Diaz—Balart, a Republican from Florida - and the nephew of Fidel Castro’s ex—wife, Mirta Diaz—Balart - said on the floor of the U.S. Congress on Tuesday that the dissident’s “condition and fate are reportedly the Castro brothers’ doing.”

U.S. Sen. Bill Nelson, of Florida, said in his own statement that “freedom—loving people everywhere should hold the Cuban regime responsible for the fate of Orlando Zapata Tamayo.”

“His reported death today is a sad reminder of the tragic cost of oppression and a dictatorship that devalues human life,” Mr. Nelson said.

Democratic U.S. Rep. Kendrick Meek, also of Florida, noted that Amnesty International declared Zapata Tamayo a “prisoner of conscience” in 2003.

“The Cuban government’s stunning lack of respect for human rights was highlighted by Orlando as much in his life as in his death,” Mr. Meek alleged in a statement.

More In: International | News