HAVANA (AFP) — Cuba said it thwarted gunmen trying to infiltrate from the United States as its coastguard opened fire Wednesday at a Florida-registered speedboat near its shores, killing four people and wounding six.

The clash was a new source of tension with Washington as the communist-ruled nation endures intense US pressure following the capture of Venezuelan leader Nicolas Maduro.

Havana’s interior ministry said people arrested after an exchange of gunfire with the boat claimed they “intended to carry out an infiltration for the purposes of terrorism.”

The ministry said assault rifles, handguns, Molotov cocktails and other military-style gear were found on the vessel and the 10 occupants were all Cubans living in the US.

US Secretary of State Marco Rubio said Washington was seeking its own facts about the shooting and would “respond accordingly.”

“We’re not going to base our conclusions on what they’ve (Cuba) told us, and I’m very, very confident that we will know the full story of what happened here,” Rubio told reporters while on a trip to the Caribbean nation of St. Kitts and Nevis.

“As we gather more information, then we’ll be prepared to respond accordingly,” he said.

The attorney general of Florida, which lies just 160 kilometers from Cuba across the Florida Straits, ordered an investigation into the killings.

The Cuban interior ministry earlier said the coast guard encountered the “illegal” US vessel, whose registration number it gave as FL7726SH, one nautical mile from Cayo Falcones island off Cuba’s northern coast.

As the coast guard vessel approached, “shots were fired from the illegal speedboat,” injuring the commander of the Cuban vessel, the ministry said.