HAVANA, Cuba (AP) — 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, fellow dissidents said. He was 60.

Elizardo Sanchez, a human rights advocate on the island and de facto spokesperson for Cuba's small opposition, said he confirmed Paya's death with his associates in the city of Bayamo, 500 miles (800 kilometres) east of the capital.

"It was an accident early in the afternoon," Sanchez said.

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."

The electrical engineer gained international fame as the top organiser 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 US 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 non-violent 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 mobilise 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.