Many of the 53 Cuban prisoners freed from jail under a historic US-Cuba accord remain bound to the justice system, their freedom conditional and subject to being returned to jail at any moment, dissident leaders say.

While they doubt Cuba's communist government would risk running afoul of the United States by returning former prisoners to jail, they say the 53 released are not entirely free.

Of 38 people released last week, about one-third are subject to "conditional release," meaning they have to periodically report to the courts supervising their cases, said the dissident Cuban Commission of Human Rights and National Reconciliation.

Another third were released on parole, requiring them to serve out their terms outside prison but unable to leave the country, it said.

Others were simply freed pending trial, or had their sentences altered. Virtually all can be returned to jail for minor offenses.