Miami, Florida - President Donald Trump on Wednesday reacted to the indictment of Cuba's former leader Raúl Castro on murder charges amid increased speculation that the US will soon try to topple the communist state.

Trump hailed the indictment on Wednesday as a "very big moment" but played down prospects of moving on Cuba, whose economy has been in a deepening crisis for months amid a US oil blockade.

"There won't be escalation. I don't think there needs to be. Look, the place is falling apart. It's a mess, and they sort of lost control," he told reporters.

The charges against the former president – who at 94 years old remains influential in Cuban politics – stem from the deadly 1996 downing of two civilian planes manned by anti-Castro pilots.

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Castro is the younger brother of Fidel Castro, the late iconic US nemesis who led Cuba's 1959 communist revolution.

"We expect that he will show up here by his own will or by another way and go to prison," acting Attorney General Todd Blanche told a news conference in Miami attended by cheering Cuban-Americans.

In addition to murder, Castro has been charged with conspiracy to kill Americans and destruction of aircraft.

The US government previously seized on a domestic indictment to justify military action in January that toppled and seized Venezuelan President Nicolas Maduro, a staunch ally of Cuba.