HAVANA, Jan 14 (Reuters) - Cuban President Miguel Diaz-Canel stated on Tuesday that his government would release 553 prisoners "gradually" following discussions with the Vatican, a move revealed shortly after the Biden administration declared it would relax a series of sanctions on the island. Cuba commended Biden's choice to ease restrictions as "appropriate," yet indicated that the measures could be insufficient and delayed, hinting that future U.S. administrations might overturn them.