Havana, Cuba - A US-based man identified as one of those killed by the Cuban coast guard in a shootout had wanted to incite a coup against the government, a political ally told AFP on Thursday.

Cuba's Coast Guard killed one American and wounded another as it opened fire on Florida-registered speedboat on Wednesday. In total four people on board were killed, with another six wounded.

The incident came amid increasingly aggressive moves made by President Donald Trump and his administration against Cuba and its people, who are suffering under a suffocating blockade.

On Thursday, Cuba's deputy foreign minister Carlos Fernandez de Cossio said Washington had "expressed willingness to cooperate in clarifying these regrettable events."

Donald Trump Trump reportedly considering order to force banks to verify customers' citizenship

Havana said all those on board the US boat were Cubans living in the US, which has received several waves of emigration from the island since the 1960s.

A political ally of one of those killed, Michel Ortega Casanova, told AFP that Ortega Casanova had spoken often of wanting to free his homeland.

"His goal was to go and fight against a criminal and murderous narco-tyrannical (government), to see if that would spark the people to rise up," said Wilfredo Beyra, head of the Cuban Republican Party in Tampa, Florida.

Beyra said he had warned Ortega Casanova, reported to be a 54-year-old truck driver, now was "not the time to take such action" but could not dissuade him.

Cuban authorities said a coast guard vessel came under fire from the speedboat around one nautical mile from Cuba's north shore, adding that assault rifles, handguns, Molotov cocktails, and military-style gear were all found onboard.

The response from the Trump administration was muted.

Secretary of State Marco Rubio, who was on a Caribbean visit, said that Washington was conducting its own investigation and would "respond accordingly."

Politicians Graham Platner builds up lead in Maine Senate race poll that spells serious trouble for Susan Collins

He insisted that the US had no hand in the confrontation.

The interior ministry said most of those on the speedboat had records in Cuba for "criminal and violent activity," and that another man sent from the US to take part in the operation was arrested on Cuban soil and confessed.

A US official also said some on the boat had criminal records, and added that an American citizen who was injured was receiving medical care in Cuba.

Beyra told AFP that several groups in Florida, home to over one million Cubans, "openly declare that they are willing, through military training, to fight for the freedom of their homeland."

He said he also knew one of the men identified by Havana as being wounded, Leordan Enrique Cruz Gomez, whom he met at a political event.

President Donald Trump has branded Cuba a "failed nation" and an "extraordinary threat" to US national security.

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 staged a violent coup in Venezuela and seized control of its oil exports.

Havana had previously relied on Venezuela for about half of its fuel needs.

After an outcry from Caribbean leaders, worried that starving 9.6 million Cubans of oil would cause the economy to collapse, the US said Wednesday it would allow limited shipments of Venezuelan oil for commercial and humanitarian use.

The Treasury Department said the Venezuelan oil would need to go through private businesses and not the Cuban government.