President Miguel Diaz-Canel said on Thursday that Cuba will defend itself against "terrorist and mercenary aggression," a day after Havana said it had killed four exiles aboard a Florida-registered speedboat that entered Cuban waters and opened fire on a patrol.
The Cuban government said the people on the speedboat in Wednesday's incident were anti-government Cubans, some of whom were previously wanted for plotting attacks. Six people on the speedboat were wounded, Cuba says.
"Cuba does not attack nor threaten," Diaz-Canel wrote on X. "We have stated this on repeated occasions and reaffirm it today: Cuba will defend itself with determination and firmness."
The incident took place at a time of heightened tensions with the United States, which has blocked oil shipments to the island to pressure the Communist-run government, after capturing and jailing Venezuelan President Nicolas Maduro, an ally of Cuba.
The fuel shortages have hit transport and worsened power cuts on the Caribbean's largest island, where the electricity grid relies on imported oil.
Venezuela had been Cuba's top oil supplier, but has not sent shipments since December, Reuters reported.
The UN has warned of a humanitarian crisis if Cuba's energy needs are not met.
On Thursday, Russia - one of Cuba's last oil suppliers, though it has not given a date for its next shipment - called for restraint and called the incident an "aggressive provocation by the United States".
US Secretary of State Marco Rubio said his government was going to independently investigate the incident.
"We're still gathering facts," he told reporters. "We don't generally make decisions in the United States on the basis of what Cuban authorities are saying."
