The US has imposed fresh sanctions on six more ships said to be carrying Venezuelan oil, a day after seizing a tanker off the country's coast.

Sanctions have also been placed on some of Venezuelan President Nicolás Maduro's relatives and businesses associated with what Washington calls his illegitimate regime.

White House press secretary Karoline Leavitt told reporters the seized vessel, called the Skipper, had been involved in "illicit oil shipping" and would be taken to an American port.

Caracas has described it as an act of "international piracy".

It marks a sharp escalation in the US pressure campaign against Maduro, which has seen dozens killed in strikes on boats alleged to have been carrying drugs from Venezuela. In recent months American warships have been moving into the region.

The Trump administration has accused Venezuela of funnelling narcotics into the US. Venezuela - home to some of the world's largest proven oil reserves - has, in turn, accused Washington of seeking to steal its resources. Maduro vowed on Wednesday that Venezuela would never become an "oil colony".

But the White House press secretary told reporters on Thursday that the US was committed to both "stopping the flow of illegal drugs" into the country and enforcing sanctions.

She would not be drawn on whether the US planned to seize more ships transporting Venezuelan oil.

"We're not going to stand by and watch sanctioned vessels sail the seas with black market oil, the proceeds of which will fuel narco-terrorism of rogue and illegitimate regimes around the world," Leavitt said.

She added that the US planned to seize the oil on board the Skipper, after the necessary legal process.

Leavitt also said Trump would not be concerned "at all" to hear Russian President Vladimir Putin had called Maduro earlier in the day to offer Moscow's support "in the face of growing external pressure".

US Treasury Secretary Scott Bessent later said that imposing sanctions on three nephews of Maduro's wife, alongside a number of businesses and ships, would tackle the leader's "dictatorial and brutal control".

In a post on X, he said the Trump administration was "holding the regime and its circle of cronies and companies accountable for its continued crimes".

On Wednesday, the White House released dramatic video footage of the raid that showed camouflaged soldiers dropping down on to the Skipper from a helicopter, and walking its deck, weapons drawn.

The Venezuelan government strongly denounced the seizure, with Maduro saying the US "kidnapped the crew" and "stole" the ship.

"They have ushered in a new era," the Venezuelan president said in a speech on Thursday. "The era of criminal naval piracy in the Caribbean."

Interior Minister Diosdado Cabello called the US "murderers, thieves, pirates" and added that this was how the country had "started wars all over the world".

The US treasury department sanctioned the Skipper vessel in 2022, CBS reported, for alleged involvement in oil smuggling that generated revenue for Hezbollah and the Islamic Revolutionary Guard Corps-Quds Force.

The US had ramped up its military presence in the Caribbean Sea, which borders Venezuela to the north, in the days before the raid.

It involved thousands of troops and USS Gerald Ford - the world's largest aircraft carrier - being positioned within striking distance of Venezuela. (BBC)

Update news