HAVANA/HOUSTON, Jan 13 - Cubans are bracing for impact after U.S. President Donald Trump vowed to cut off a lifeline of Venezuelan oil from reaching Cuba, setting up a siege scenario for an island already reeling from crippling blackouts and shortages.

Venezuela, once the island's top supplier, has not sent crude or fuel to Cuba for about a month, according to shipping data and internal documents from state company PDVSA, with cargoes falling off due to a U.S. blockade even before the U.S. capture of Venezuelan leader Nicolas Maduro in early January.