HAVANA—Cuban activist Oswaldo Paya, who spent decades speaking out against the communist government of Fidel and Raul Castro and became one of the most powerful voices of dissent against their half-century rule, died Sunday in a car crash. He was 60.

Paya and a Cuban man described by media as a fellow activist, Harold Cepero Escalante, died in a one-car crash in La Gavina, just outside the eastern city of Bayamo, Cuban authorities said. A Spaniard and a Swede also riding in the car were injured.

Cuba’s International Press Center told The Associated Press that witnesses said the driver of the rental car lost control and struck a tree. Police are investigating.

“This Sunday has been a day of mourning. A terrible tragedy for his family and a loss for the opposition movement,” said Elizardo Sanchez, a human rights advocate and de facto spokesperson for Cuba’s small opposition. “He was a prominent leader. He dedicated years of his life to fighting for democracy.”

Paya’s home is in Havana and it was not immediately clear why he was near Bayamo, 800 kms east of the capital.

He is the second leading Cuban dissident to die in the last year, after Laura Pollan, co-founder of the protest group Ladies in White, died of heart failure in October.

Paya, who drew strength from his Roman Catholic roots as he pressed for change in his homeland, continued to voice his opposition after Fidel resigned due to illness in early 2008, calling the passing of the presidency to younger brother Raul a disappointment.

“The driving force of society should be the sovereignty of the people, not the Communist Party,” Paya wrote after the new parliament chose Raul Castro as head of state and government. “The people of Cuba want changes that signify liberty, open expression of their civil, political, economic and social rights.”

Paya, an electrical engineer, gained international fame as the top organizer of the Varela Project, a signature gathering drive asking authorities for a referendum on laws to guarantee civil rights such as freedom of speech and assembly.

Shortly before former U.S. President Jimmy Carter’s visit to Cuba in May 2002, Paya delivered 11,020 signatures to the island’s parliament seeking that initiative. He later delivered a second batch of petitions containing more than 14,000 signatures to the National Assembly, Cuba’s parliament, posing a renewed challenge to the island’s socialist system.

The Varela Project was seen as the biggest nonviolent campaign to change the system the elder Castro established after the 1959 Cuban revolution.

The government set aside the first batch of signatures and launched its own, successful petition drive to enshrine the island’s socialist system as “irrevocable” in the Cuban constitution.

Paya continued his efforts, saying it was more important to mobilize Cubans to demand human rights than to win government acceptance of the project. However, his influence waned notably in his final years as younger activists and bloggers like Yoani Sanchez gained international headlines.

Paya and other longtime opposition figures were described disparagingly in leaked, confidential U.S. diplomatic cables as old, riven by petty rivalries and out of touch with the island’s youth.

“They have little contact with younger Cubans and, to the extent they have a message that is getting out, it does not appeal to that segment of society,” said one cable from 2009, which was made available by WikiLeaks the following year.

Cuba’s government routinely dismisses opponents as American stooges bankrolled by Washington to undermine the revolution. The revelation that U.S. diplomats privately held so low a regard for the opposition was a major embarrassment for many.

Oswaldo Jose Paya Sardinas was born on Feb. 29, 1952, the fifth of seven siblings in a Catholic family.

Paya started his studies at a public elementary school in Havana’s Cerro neighbourhood, but later transferred to a prestigious Catholic school that was shut down shortly after the revolution.

Even from a young age, Paya openly criticized the communist government. He was still a teenager when he was sent as punishment in May 1969 to complete his military service at a work camp on Cuba’s small Isle of Youth, then called the Isle of Pines.

He finished his high school-level studies at a night school, and enrolled at the University of Havana with a major in physics. But when authorities learned Paya was a practicing Christian who rejected Marxism, he had to leave the university and took night courses in telecommunications.

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In the early 1980s, Paya began work for the Public Health Ministry as a specialist in electronic medical equipment — a job he maintained late in life despite his dissident activities — repairing such things as X-ray machines and incubators for premature infants.

He married Ofelia Acevedo in 1986 in a Catholic Church wedding — a practice tolerated but considered extremely odd in those years, as Cuba was still an atheistic state. They had three children together.

Paya became an activist in the late 1980s when he founded the non-governmental Christian Liberation Movement, which emphasized peaceful, civic action. He was detained in March 1990, but released after a few days.

Shortly thereafter, Paya’s group made a public “Call for National Dialogue” between Cubans on the island and in exile.

Around the same time, Paya launched the first of several early signature gathering drives aimed at forcing a democratic opening on the island. That effort ended with failure and an insult painted on his house: “PAYA: CIA AGENT.”

He began writing the text of the Varela Project in 1996 and the Christian Liberation Movement began collecting signatures in 1998.

Just days after Paya submitted the first batch of Varela Project petitions in May 2002, Carter praised the democratic effort in a speech broadcast live — and as earlier promised by Castro, uncensored — to the Cuban people.

In late 2002, the European Union awarded Paya its top human rights prize and pledged to support his efforts to bring democracy to his homeland. Named after the late-Soviet dissident Andrei Sakharov, the prize is awarded annually by the 15-member union’s parliament to defenders of human rights and democracy.

Through his years of activism, Paya always underscored his religious upbringing as the foundation for his convictions.

“The rights that we demand in the Varela Project are enunciated in the constitution. But we also have them because we are human beings, sons of God,” Paya said after turning in the second batch of petitions. “And because of that, we will continue demanding them for all Cubans, with the faith that we will achieve them.”

Paya’s death was also noted by the Cuban exile diaspora in the U.S. and elsewhere.

“Through his leadership, Oswaldo inspired countless democracy advocates who have embraced and carried forth his vision of non-violent political change,” read a statement from the Cuba Study Group, which encourages political and economic change in Cuba as well as more U.S. exchanges with the island. “Oswaldo’s memory and legacy lives on in their work.”