US Secretary of State Marco Rubio said Washington had nothing to do with the clash and would “respond accordingly” after investigating.
The attorney general of Florida, which lies about 160km from Cuba across the Florida Straits, also ordered an investigation into the killings.
The Cuban interior ministry has released what it says are the names of seven of the people on the boat and said most of the 10 aboard had records in Cuba for “criminal and violent activity”.
Another man sent from the United States to take part in this operation was arrested on Cuban soil and confessed, it added.
The Cuban government frequently reports incursions by speedboats from the United States into its territorial waters but deadly clashes are rarer.
Incursion incidents are often related to people-smuggling to the United States or drug trafficking, and have included chases, shootouts and armed attacks on border guards.
Venezuelan oil
The latest clash comes as Cuba is reeling from US economic pressure.
Cuba’s communist government lost one of its key diplomatic supporters – and a vital source of fuel for the country – in January when US forces toppled Venezuelan leader Nicolas Maduro, effectively taking control of Venezuelan oil exports.
The country had relied on Venezuela for about half of its fuel needs.
Amid an outcry from Caribbean leaders, worried that starving 9.6 million Cubans of oil would cause the economy to collapse, the Trump administration said it would allow limited shipments of Venezuelan oil for “commercial and humanitarian use”.
The announcement came during a summit of Caribbean nations attended by Rubio, a Cuban-American who has spent his career calling for the downfall of Havana’s communist leadership.
The US Treasury Department said the Venezuelan oil would need to go through private businesses and not the Cuban government or the military apparatus that controls much of the island’s economy.
Mexico dispatched two military vessels carrying nearly 2200 tons of aid to the island this week – its second aid shipment in under a month.
Canada also announced C$8 million ($9.7m) in aid.
- Agence France-Presse