President Donald Trump has said he is restoring some travel and economic restrictions on Cuba that were lifted by Barack Obama's administration.
He challenged the communist government of Raul Castro to negotiate a better deal for Cubans and Cuban-Americans.
Announcing the changes during a speech in Miami, Mr Trump said Cuba had secured far too many concessions from the US in the "misguided" deal but "now those days are over".
He said penalties on Cuba would remain in place until its government releases political prisoners, stops abusing dissidents and respects freedom of expression.
"America has rejected the Cuban people's oppressors," Mr Trump said in a crowded, sweltering auditorium. "They are rejected officially today - rejected."
Though Mr Trump's announcement stops short of a full reversal of the Cuba rapprochement, it targets the travel and economic engagement between the countries that has blossomed in the short time since relations were restored.
The goal is to halt the flow of US cash to the country's military and security services in a bid to increase pressure on Cuba's government.
Embassies in Havana and Washington will remain open. US airlines and cruise ships will still be allowed to serve the island 90 miles south of Florida.
The "wet foot, dry foot" policy, which once let most Cuban migrants stay if they made it to US soil but was ended under Mr Obama, will remain terminated. Remittances to Cuba will not be cut off.
But individual "people-to-people" trips by Americans to Cuba, allowed by Mr Obama for the first time in decades, will again be prohibited.
Just as we were making progress w/ #Cuba, Trump decides to once again turn back the clock. He's not creating policy, he's dismantling policy— Jose Hernandez (@MrJoseHernandez) June 16, 2017
And the US government will police other such trips to ensure there is a tour group representative along making sure travellers are pursuing a "full-time schedule of educational exchange activities".
Mr Trump described his move as an effort to ramp up pressure to create a "free Cuba" after more than half a century of communism.
"I do believe that end is in the very near future," he said.
His move was a direct rebuke to Mr Obama, for whom the diplomatic opening with Cuba was a central accomplishment of his presidency. The new president's action is broadly opposed by American business groups.
"US private sector engagement can be a positive force for the kind of change we all wish to see in Cuba," said Myron Brilliant, the US Chamber of Commerce executive vice president and head of international affairs.
"Unfortunately, today's moves actually limit the possibility for positive change on the island and risk ceding growth opportunities to other countries that, frankly, may not share America's interest in a free and democratic Cuba that respects human rights."
In Cuba, Granma, the official organ of the nation's Communist Party, covered Friday's speech in a real-time blog, saying: "Trump's declarations are a return to imperialist rhetoric and unilateral demands, sending relations between Havana and Washington back into the freezer."