Cuba’s government said Wednesday that its military forces killed four Cuban-born U.S. residents after intercepting a Florida-registered speedboat that entered Cuban territorial waters in what officials described as a thwarted armed infiltration.

In a statement, Cuba’s Interior Ministry said the vessel was carrying 10 armed individuals who, according to preliminary accounts from those detained, intended to carry out a “terrorist” operation on the island.

Authorities said they seized assault rifles, handguns, Molotov cocktails, bulletproof vests, telescopic sights and camouflage uniforms from the boat.

The ministry reported that the confrontation occurred Wednesday morning about one nautical mile northeast of the El Pino channel off Cuba’s northern coast. According to officials, a Cuban border guard vessel approached the speedboat for identification when those aboard allegedly opened fire, injuring the commander of the Cuban patrol craft. Six people on the Florida-registered boat were also reported injured.

All 10 individuals aboard the vessel were described by Cuban authorities as Cuban nationals residing in the United States.

U.S. Secretary of State Marco Rubio, speaking from Saint Kitts and Nevis, where he was attending a meeting with Caribbean leaders, said the United States would conduct an independent investigation before issuing any formal response.

“We’re going to find out exactly what happened here, and then we’ll respond accordingly,” Rubio said, noting that a shootout at sea was “highly unusual.” He added that both the U.S. Department of Homeland Security and the United States Coast Guard were investigating the incident.

Cuban authorities identified one of the deceased as Michel Ortega Casanova. His brother, Misael Ortega Casanova, told The Associated Press that Michel had lived in the United States for two decades, working as a truck driver and becoming an American citizen. He described his brother’s actions as driven by an intense desire for Cuba’s freedom.

The incident marks a rare and dramatic escalation in tensions between Cuba and individuals operating from U.S. soil, as both governments move to establish the facts surrounding the deadly confrontation at sea.