Cuban prosecutors said that terrorism charges had been brought against six crew members of a US-flagged speedboat that was intercepted by Cuba's coast guard in a shootout last week.
The US-based Cuban defendants are accused of packing a boat with weapons and heading toward Cuba in hopes of destabilising the government in Havana.
The coast guard shot and killed four other people on board the boat, which came within one nautical mile of the Caribbean island's shores in the 25 February shootout.
The defendants will be "remanded into provisional detention," the attorney general's office said in a statement.
Cuban officials said the boat, registered in the United States, was carrying firearms of various calibers, including 14 rifles, 11 pistols and nearly 13,000 rounds of ammunition.
The incident occurred when a coast guard boat approached the vessel to demand identification, and they responded by opening fire.
At least two of those aboard the speedboat were US citizens, one of whom was killed.
US President Donald Trump's administration has made no secret of its desire for regime change in Cuba, imposing an energy blockade after ousting president Nicolas Maduro in Venezuela, which was the communist nation's top supplier of oil.
Last week, Cuba said the US was willing to cooperate in the investigation.
After the Cuban revolution in 1959, such infiltration attempts by armed commandos from South Florida were not uncommon.
