The US has seized a sixth tanker in the Caribbean Sea in its ongoing efforts to control exports of Venezuelan oil, officials say.

The vessel, Veronica, was boarded in a predawn operation "without incident" as it was defying President Donald Trump's "quarantine of sanctioned vessels", said the US military.

"The only oil leaving Venezuela will be oil that is coordinated properly and lawfully," the Southern Command said.

Since the US military strikes on Venezuela and seizure of its president Nicolás Maduro this month, Trump has said he plans to tap into the country's huge oil reserves.

"The Veronica is the latest tanker operating in defiance of President Trump's established quarantine of sanctioned vessels in the Caribbean," US Southern Command said in a post on social media.

It also posted a video showing Marines and sailors boarding the tanker.

Veronica, a crude oil tanker sailing under a Guyanese flag, departed empty from Venezuelan waters in early January, according to monitoring service TankerTrackers.com.

The International Maritime Organization's database shows the vessel was previously registered in Russia under different names.

Homeland Security Secretary Kristi Noem posted on social media that Thursday's tanker seizure was carried out with "close coordination with our colleagues" in the military as well as the state and justice departments.

"Our heroic Coast Guard men and women once again ensured a flawlessly executed operation, in accordance with international law," Noem added.

It suggests Washington's crackdown on the so-called dark fleet, comprising more than 1,000 vessels that transport sanctioned oil, will continue as the US works with Venezuela's interim government to control the country's oil sales.

It also comes a day after an American official said the US had completed its first sale of Venezuelan oil, valued at $500m (£373m).

Trump last week asked oil executives at the White House to invest $100bn in Venezuela's energy infrastructure. They said significant changes would be needed make the country an attractive investment.

The blockade has sharply curtailed Venezuelan oil exports, with only ships associated with Chevron and bound for the US operating as usual, according to Matt Smith, head of US analysis at Kpler.

Loadings have fallen roughly in half this month to about 400,000 barrels per day, he said.

The Veronica, a relatively small tanker with a sanctioned owner, was among about 17 ships that attempted to breach the blockade earlier this month, according to the firm.

Smith said it was unclear why vessels from the so-called dark fleet would risk seizure, but noted the financial cost of delays. "If a tanker was supposed to be moving crude and can't get through, that's money lost," he said.

He said the US quarantine had created a bottleneck of supply that would otherwise be headed to countries, mainly China.

But as the US starts selling Venezuelan oil, he said there were signs the situation was evolving with some tankers now headed to the Bahamas for storage.

The latest tanker seizure came just hours ahead of a meeting between Trump and Venezuela's opposition leader Maria Corina Machado at the White House.

Trump has previously described her as a "freedom fighter", but rejected the notion of appointing her to lead Venezuela after Maduro's removal, arguing that she lacks sufficient domestic backing. He instead backed Delcy Rodríguez, Maduro's former vice-president.

Trump describes Rodríguez as an "ally", and she has not been charged by US officials with any crimes.

Machado is expected to use her face time with Trump to try to persuade him that his decision to back Rodríguez's interim government is a mistake, and that her opposition coalition should be in charge of this transition.

A Venezuelan government envoy, too, is expected to travel to Washington on Thursday to meet US officials and take initial steps towards reopening the country's embassy, the New York Times reported.

"The emissary is reported to be a close ally and friend of the interim president, Delcy Rodríguez, who has been described as "extremely co-operative" by the White House.

On Thursday, White House press secretary Karoline Leavitt said the $500m energy deal was struck in large part because of help from Rodriguez.

She said the interim president had also confirmed that Venezuela would be releasing political prisoners from Venezuela.

"There were five Americans who were recently released this week as well," Leavitt said.

"So, the president likes what he's seeing. And we'll expect that co-operation to continue."