The Cuban authorities had said that the crash happened after Ángel Carromero, a young Spanish politician who was driving the vehicle in which Mr. Payá was traveling, lost control and hit a tree. Mr. Carromero was later arrested and sentenced to four years in prison for vehicular manslaughter.

But the independent investigation, which took a decade to complete and reviewed evidence and testimonies from several witnesses, contradicts the government’s findings. Mr. Payá’s car was hit by an official government car, causing it to crash, according to the report by the Inter-American Commission on Human Rights, which observes and investigates human rights violations across the hemisphere and is part of the Organization of American States.

Another passenger, Harold Cepero, a rights activist, was also killed.

The commission found “serious and sufficient evidence to conclude that state agents participated in the death” of the two men. “Both were subjected to various acts of violence, harassment, threats, attempts on their lives, and, finally, a car crash that caused their deaths.”

Cuban officials did not immediately respond to requests for comment. The island was excluded from participating in the Organization of American States, which brings together nations from across the continent, and which former President Raúl Castro once called an “instrument of imperialist domination.” A 2009 resolution lifted the suspension, but Cuba never rejoined.

Mr. Payá was the founder and leader of the Christian Liberation Movement, a dissident party pushing for a multiparty democracy on the island, which has been ruled by an authoritarian Communist regime for more than six decades.