San Juan, May 30 (RHC)-- Thousands of Puerto Ricans demanded the release of political prisoner Oscar Lopez Rivera, who has been locked up in U.S. prisons for 35 years -- marching through the streets of San Juan on Sunday.

Protesters also called for U.S. President Barack Obama to pardon Ocsar, who is a leader in the Puerto Rican independence movement. 

Groups in support of the island's independence are preparing for another protest on June 20th, when the United Nations will review Puerto Rico’s colonial status, and others in the coming weeks to increase the pressure for Lopez Rivera's release from prison.

Observers note that Oscar Lopez Rivera is one of the longest-held political prisoners in history — 34 years – longer than South African Nelson Mandela.

Speaking at a news conference on Sunday in San Juan, the Puerto Rican capital, the former secretary of interior of Puerto Rico, Ingrid Vila Biaggi, said: "Oscar is in prison for wanting to liberate us from the colonial status that keeps us in crisis, (therefore) his release from prison is a step to negotiate the future of Puerto Rico" with Washington.