Donald Trump says the US has "knocked out" a "big facility" in Venezuela — but has only provided vague details about what could be a major escalation in his military campaign. 

The US president initially mentioned the attack when he phoned into a right-wing radio station in New York on Friday, local time. 

"I don't know if you read or you saw — they have a big plant or a big facility where they send the, you know, where the ships come from," Mr Trump told radio host John Catsimatidis. 

"Two nights ago, we knocked that out. So we hit them very hard." 

Catsimatidis, a billionaire Republican donor, did not ask any follow-up questions about the strike and the news went largely unnoticed at the time. 

Mr Trump was questioned further by reporters in Florida on Monday, but would only say there had been a "a major explosion in the dock area where they load the boats up with drugs". 

"They load the boats with drugs, so we hit all the boats and then we hit the area," he said. 

"It's the implementation area, that's where they implement. And that is no longer around." 

Asked if the US had carried out any other strikes, Mr Trump said: "I don't want to comment." 

He also declined to say if the American military or the CIA were behind the attack. "I know exactly who it was, but I don't want to say who it was."

In October, Mr Trump confirmed he had authorised the CIA to carry out covert operations inside Venezuela.

A US strike on Venezuelan soil would be the first known land attack in the country since the Trump administration began ratcheting up pressure on its ruling regime, which Mr Trump accuses of "narco-terrorism".

Nicolás Maduro has called on the international community to oppose what he says is a US attempt to spark regime change. (AP: Ariana Cubillos)

Venezuela has not confirmed or commented on the attack. The State Department and the White House have not responded to the ABC's requests for more information.

Some social media users questioned whether a fire at a chemical facility in Maracaibo, on Venezuela's north-west coast, could have been the result of the US strike. 

The fire took place the same night Mr Trump said the strike took place. Maracaibo, Venezuela's second-largest city, has one of its largest seaports.

The company that owns the facility, Primazol, issued a statement to "categorically reject" versions of events circulating on social media, which it said were intended to hurt the reputation of the company and its founder. The company's statement did not explicitly refer to Mr Trump's comments or the US strike.