HAVANA (AP) — Cuba said Wednesday it has filed terrorism charges against six suspects it claims were aboard a Florida-flagged speedboat that is alleged to have opened fire on soldiers in waters off the island’s north coast.

The Prosecutor’s Office said in a statement that the suspects of Cuban origin remain in pretrial detention, adding that it will ensure “due process” as it continues to act “in defense of our people and the country’s institutions.”

The government has said 10 heavily armed Cubans from the U.S. who were on board the boat opened fire as they tried to infiltrate the island to commit acts of terrorism. It said that Cuban soldiers returned fire, killing four suspects.

The government unveiled items said to have been found on the boat, including a dozen high-powered weapons, more than 12,800 pieces of ammunition and 11 pistols.

Chief prosecutor Edward Robert Campbell has told The Associated Press that terrorism charges carry a possible sentence of up to 30 years in prison or even the death penalty, although Cuba has maintained a moratorium on the latter since 2003.