US President Donald Trump confirmed on Wednesday that he has authorised the CIA to conduct covert operations inside Venezuela and said he was weighing carrying out land operations on the country.

The acknowledgement of covert action in Venezuela by the US spy agency comes after the US military in recent weeks has carried out a series of deadly strikes against alleged drug-smuggling boats in the Caribbean.

US forces have destroyed at least five boats since early September, killing 27 people, and four of those vessels originated from Venezuela.

Asked during an event in the Oval Office on Wednesday why he had authorised the CIA to take action in Venezuela, Trump affirmed he had made the move.

“I authorised for two reasons, really,” Trump replied.

“Number one, they have emptied their prisons into the United States of America," he said. "And the other thing, the drugs, we have a lot of drugs coming in from Venezuela, and a lot of the Venezuelan drugs come in through the sea.”

Trump added the administration “is looking at land” as it considers further strikes in the region. He declined to say whether the CIA has authority to take action against President Nicolás Maduro.

Trump made the unusual acknowledgement of a CIA operation shortly after The New York Times published that the CIA had been authorised to carry out covert action in Venezuela.

Early this month, the Trump administration declared drug cartels to be unlawful combatants and pronounced the United States is now in an “armed conflict” with them, justifying the military action as a necessary escalation to stem the flow of drugs into the United States.

Shortly after Trump spoke, Venezuelan President Nicolas Maduro responded by accusing Washington of seeking to overthrow his government.

"No to war in the Caribbean...No to regime change...No to coups d'etat orchestrated by the CIA," the leftist leader said in an address to a committee set up after Washington deployed warships in the Caribbean for what it said was an anti-drug operation.

Maduro had on Wednesday ordered military exercises in the country's biggest shantytowns and said he was mobilizing the military, police and a civilian militia to defend Venezuela's "mountains, coasts, schools, hospitals, factories and markets." (Agencies)