Donald Trump said on Monday that the US had "hit" an area in Venezuela where boats are loaded with drugs, marking the first known time Washington has carried out land operations in Venezuela since a pressure campaign began against President Nicolas Maduro's government.

"There was a major explosion in the dock area where they load the boats up with drugs," Trump said. "We hit all the boats, and now we hit the area ... it's the implementation area. That's where they implement, and that is no longer around."

It was not immediately clear what target was hit nor which part of the US government acted.

Asked if the CIA had carried out the attack, Trump said: "I don't want to say that. I know exactly who it was but I don't want to say who it was."

CNN, citing sources, reported on Monday that the CIA had carried out a drone strike earlier this month on a port facility on the coast of Venezuela.

The strike targeted a remote dock that the US believed was being used by the Venezuelan gang Tren de Aragua to store drugs and move them onto boats for onward shipping, according to CNN.

Trump has previously said that he has authorized the CIA to carry out covert operations in Venezuela.

On a radio show last week, Trump made vague comments about an apparent US operation against a "big facility" in Venezuela.

The Central Intelligence Agency, the White House and the Pentagon have not publicly elaborated on those comments and declined to comment on questions posed by Reuters. The Venezuelan government has not commented on the incident Trump described and there have been no independent reports from Venezuela of it.

Primazol, a chemical plant in Zulia state which suffered a fire on Christmas Eve, has denied online rumors that the blaze was what Trump alluded to in his comments. The company also said the fire was quickly extinguished and was under investigation. Nearby residents told Reuters they heard an explosion, saw the fire and smelled chlorine.

The Venezuelan communications ministry, which handles all press requests for the government, did not immediately respond to a request for comment on Monday.