US President Donald Trump threatens "full and complete embargo" and sanctions on Cuba if its troops do not cease operations in Venezuela.

Trump said via Twitter that if Cuban troops and militia do not immediately cease military operations in Venezuela, the US will impose embargo together with "highest-level" sanctions.

Washington has long maintained that Havana exerts undue influence in Venezuela, with US Secretary of State Mike Pompeo attacking Cuba as an "imperialist power" last month in a cruel reversal of terms.

"No nation has done more to sustain the death and daily misery of ordinary Venezuelans, including Venezuela's military and their families, than the communists in Havana," Pompeo said in a March 11 statement.

However, Cuba has been under a US embargo since the early 1960s, following its failure to overthrow the Cuban government under Fidel Castro in 1959. The embargo has been widely condemned internationally, and attempts at the United Nations to issue official condemnations of the embargo have seen such drastic contrasts as last October's vote of 189-2, with only the US and Israel voting against the measure.

It's unclear if there are any Cuban troops in Venezuela at all, or how many, but the island nation has provided tens of thousands of doctors to Venezuela since former leader Hugo Chavez established close relations with Cuba in the early 2000s.

Cuba has 31,000 doctors and dentists in the country and has provided training for 40,000 Venezuelan medical personnel in exchange for 100,000 barrels of oil per day — a commodity sorely needed in Cuba due to the US blockade.

Cuba's Minister of Foreign Affairs, Bruno Rordriguez, tweeted late Tuesday that US national security adviser John Bolton "is pathological liar who misinforms Trump. There are no Cuban troops in #Venezuela; nor are there any Cubans taking part in military or security operations there. Only medical staff in humanitarian mission. I strongly reject Trump's total blockade threat."