The US has charged former Cuban leader Raúl Castro with conspiracy to kill US nationals and other crimes over the downing of two planes between Cuba and Florida in 1996.

The case unveiled on Wednesday – a revival of charges originally from 2003 – accuses Castro and five others of shooting down aircraft belonging to Cuban American group Brothers to the Rescue and killing four people, including three Americans.

Castro, now 94, was the head of the country's armed forces and faced international condemnation over the crash.

As the US seeks to exert increasing pressure on Cuba's communist rule, President Miguel Díaz-Canel called the charges "a political manoeuvre, devoid of any legal foundation".

Speaking at Freedom Tower in Miami, Acting Attorney General Todd Blanche announced that the US would also charge Castro with destruction of aircraft, and four individual counts of murder over the deaths of Armando Alejandre Jr,  Carlos Alberto Costa, Mario Manuel de la Peña, and Pablo Morales.

"The United States, and President Trump, does not, and will not, forget its citizens," Blanche said.

The justice department's new charges take aim at a key figurehead of Cuba's communist leadership when it is facing intense US pressure to make significant political and economic reforms to its one-party rule there.

"I think the strategy is to increase the pressure gradually to the point where the Cuban government will give in and surrender at the bargaining table," said Wiliam LeoGrand, a expert on Latin American politics at American University.

The US has issued sanctions on the country and imposed a blockade on oil to Cuba that has resulted in blackouts and food shortages.

Earlier on Wednesday, US Secretary of State Marco Rubio issued a message to the Cuban people timed to the country's independence day.

"President Trump is offering a new path between the US and a new Cuba," Rubio said.

Rubio told citizens of the island that a Cuban military-run conglomerate known as GAESA is primarily responsible for the blackouts and food shortages that the country continues to endure.

GAESA owns or operates most of the lucrative parts of the Cuban economy from the ports to the petrol pumps to 5-star hotels.

In response to Rubio's message, Díaz-Canel accused the US of lying and imposing a collective punishment on the Cuban people.

Díaz-Canel also said that the indictment of Castro was being used to "justify the folly of a military aggression against Cuba" and accused the US of distorting the facts around the downing of the plane.

He claimed that Cuba acted in "legitimate self-defence within its jurisdictional waters".

Asked by reporters about the prospects of bringing Castro to the US to face charges, Blanche responded that there was a warrant for his arrest.

"We expect he will show up here, by his own will or another way," he said.

Nearly 95 years old, Castro remains an influential figure, acknowledged on the island as the surviving "leader of the Cuban Revolution".

He has relinquished his active government and party roles, but during his 2008-2018 presidency, he and former US president Barack Obama presided over a short-lived thaw in Washington-Havana relations.

Blanche said he would "not compare cases" between Castro's and that of Venezuelan President Nicolás Maduro.

In January, the US staged a military operation to seize Maduro and bring him to the US, after the justice department indicted him.

US President Donald Trump was asked about the political aspect of the indictment.

"A lot of those people are related to me in the sense that I've had such a great relationship with Cuban-Americans," Trump said. "On a humanitarian basis, we're here to help."

The Miami centre where US officials announced the indictment of Raúl Castro was full of Cuban Americans, mostly representing Cuban exile organisations that have for decades led opposition of the Cuban government from within the United States.

Surrounded by pictures of the four people who died in the 1996 crashes, many at the Miami event described being thrilled by the news.

"It was time, 67 years of that murderous regime," said Isela Fiterre. "Raúl Castro did not merely kill four individuals. Over the course of many years, he has killed countless people," Fiterre said.

She said it is never too late for justice and that she is grateful to the Trump administration for taking this step.

Another attendee, Mercedes Puid-Soto, echoed those sentiments.

"I feel very happy. Justice has been served," she said. "It's very important that the families can close that chapter, and we Cubans too."

Still looming over Blanche's announcement was the answer to "whether the Trump administration will use this indictment in a similar way that it used the indictment against Maduro, as a justification to carry out a military operation under the cover of a law enforcement action," said Roxanna Vigil, an international affairs fellow at the Council on Foreign Relations.

"It's unlikely that the Cuban regime will surrender to the United States without a fight," Vigil noted. "And any move that includes working with the Cuban regime would be very difficult for the Cuban diaspora in the United States to accept."

US and Cuban representatives, including Raúl Castro's grandson Raúl Guillermo Rodriguez Castro, have held "conversations" in recent months, but US charges against the former president are unlikely to smooth these contacts.

On the contrary, the Cuban side showed signs of further entrenching into its "no surrender, no concessions" position against US pressure, with Cuban state media outlets blasting what they called the "false accusations".

Tracking data shows several flights by US Navy reconnaissance jets and drones during the last week.

Havana's foreign minister says a report that it has acquired attack drones is part of justification for US "aggression".

Charges could come as soon as next week in a case reportedly focused on Cuba's downing of two planes in 1996.

The reported visit to Havana came after the US renewed an offer of aid to ease the effects of its oil blockade.

The new measures come on top of a US blockade of oil to Cuba that has caused widespread blackouts and fuel shortages.