WASHINGTON — President Trump on Tuesday accused Cuba of aiding the government of President Nicolás Maduro of Venezuela, who the administration evidently hoped would be ousted by day’s end, warning that the United States would impose an embargo and additional sanctions on the country if Cuba did not end its support.

“If Cuban Troops and Militia do not immediately CEASE military and other operations for the purpose of causing death and destruction to the Constitution of Venezuela,” Mr. Trump wrote on Twitter, “a full and complete embargo, together with highest-level sanctions, will be placed on the island of Cuba.”

At the same time, the Trump administration reaffirmed its demand for the immediate installation of Juan Guaidó, the opposition leader, as Mr. Maduro’s successor.

Secretary of State Mike Pompeo said in an interview with CNN that Mr. Maduro had planned to flee to Cuba on Tuesday morning, but was urged by the Russian government to stay. “He was headed to Havana,” Mr. Pompeo said, without elaborating on how the administration knew about Mr. Maduro’s destination or his communications with the Kremlin.