More than 2000 prisoners are slated to be released beginning on Friday as part of Cuba's state-run media called a "sovereign and humanitarian" gesture, the largest such amnesty in 10 years.
The US said it was closely monitoring whether those it deems to be political prisoners would be among the liberated.
The question of political prisoners has long been a major sticking point in negotiations between Washington and Havana. The release of all, or the majority, of political prisoners would be seen as a major concession on Cuba's part in ongoing talks between the two countries.
A steady stream of men and women could be seen leaving the La Lima prison in Guanabacoa, just outside Havana, through the morning on Friday. Reuters spoke with several who had been pardoned of common crimes ranging from theft to bribery, but none had been involved in political anti-government protests.
"Long-live freedom," shouted one man, convicted of theft, as he embraced his sister, waiting for him outside the prison gates. Others left more quietly, some in tears, holding a single white slip of paper that stated the reason for their discharge was a pardon.
The Cuban government has consistently rejected any suggestion it makes decisions under US pressure.
Neither the US nor the Vatican, which was involved in prior amnesties, were mentioned in state-run media reports outlining Thursday evening's announcement.
Human rights groups, some financed by the US government, say Cuba is holding hundreds of political prisoners, with estimates varying, and promised scrutiny of the prisoner release process.
Cuba has repeatedly denied it holds political prisoners. Island authorities say those jailed during anti-government protests are found guilty of crimes including public disorder, resisting arrest, robbery and vandalism.
The Cuban Observatory for Human Rights, a Madrid-based group that has received US funding, said that by noon on Friday it had yet to register the release of any so-called "prisoners of conscience."
Cuba generally does not publish a list of the names of prisoners released during such amnesties, further complicating corroboration by human rights groups.
Sources told Reuters several prisons around Havana, and elsewhere in the Cuban provinces, had begun releasing prisoners.
In late 2015, the Cuban government pardoned 3522 prisoners to coincide with Pope Francis' visit to the island during a warming of US-Cuba relations under then-president Barack Obama.
Cuba in March freed 51 prisoners under an agreement with the Vatican.
The rights groups said that some, but not all, of those released last month were among those they considered political prisoners.
