The threat against Havana is the latest in a series of Trump administration pledges aimed at Cuba's communist regime.
Trump says the war in Iran is the top priority, but adds that Cuba "is ready" and that Secretary of State Marco Rubio - whose parents are from Cuba - will be given the main responsibility.
They want to negotiate, so I'll send Marco there and we'll see how it goes, Trump tells an American media company.
Cuba is suffering severely under U.S. sanctions and is in the midst of a widespread energy crisis after important oil supplies from Venezuela were cut off.
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