Prominent Cuban opposition leader Oswaldo Paya was killed in a car accident late Sunday, a fellow dissident and officials said.
The 60-year-old was travelling near the town of Bayamo in eastern Cuba when the car he was in hit a tree, dpa quoted authorities as saying.
At the head of the dissident Christian Liberation Movement, Paya waged a long-standing campaign of legal initiatives to reform the systems put in place by revolutionary leader Fidel Castro.
He was nominated several times for the Nobel Peace Prize and awarded the European Parliament's Sakharov Prize for freedom of thought in 2002.
In 1998, he launched a petition known as the Varela Project, named after a Cuban religious leader, to call for greater civil liberties, including the right to association and freedom of expression.
The text was dismissed as a "strategy of subversion" by the government, but it was signed by more than 25,000 people, well over the 10,000 required under the constitution to be considered by lawmakers.
Elizardo Sanchez, founder and leader of the Cuban Human Rights and National Reconciliation Commission, who confirmed Paya's death, said it was an "irrevocable loss" for the country's pro-democratic movement.
"He was without a doubt the most important leader of the opposition in Cuba," Sanchez said. Harold Cepero, another dissident in the car, was also killed in the accident while the two remaining passengers, a Spaniard and a Swede, suffered minor injuries.
Paya, a practising Catholic, had an ambivalent relationship with the church, which he accused of making compromises in its own relations with the Cuban government. But he welcomed the pope's visit in late March, which some dissidents in the strongly Catholic, communist country criticized as an endorsement of the regime.
In an online newsletter, Cuba's Roman Catholic Church said of Paya, "Notwithstanding the differences in objectives and methodologies with regards to the nation's future, we note that we always considered him an honest person, an exemplary father, a Catholic of integrity, a good Cuban and a politician who invariably acted according to his conscience."