US President Donald Trump has ordered "a total and complete" blockade of all sanctioned oil tankers entering and leaving Venezuela - a move denounced by Caracas as "warmongering threats".

Trump wrote that Venezuelan President Nicolás Maduro's government had been designated a foreign terrorist organisation (FTO), which had also engaged in "Drug Smuggling, and Human Trafficking".

His remarks come after the US seized an oil tanker off the coast of Venezuela last week, a significant action in light of the South American nation's reliance on oil.

The US has also recently conducted deadly strikes on alleged Venezuelan drug-smuggling boats and has significantly built up its naval presence nearby.

Trump's post did not give further details of how the wide-ranging blockade on sanctioned oil tankers would be enforced.

As of last week, more than 30 of the 80 ships in Venezuelan waters or approaching the country were under US sanctions, according to data compiled by TankerTrackers.com.

Multiple new US sanctions on ships allegedly carrying Venezuelan oil were imposed after the tanker was seized. Sanctions were also placed on some of President Maduro's relatives and on businesses associated with what the US called his illegitimate regime.

In his Truth Social post on Tuesday, Trump wrote that Venezuela was "completely surrounded by the largest Armada ever assembled in the History of South America". He added that it would "only get bigger" and "be like nothing they have ever seen before".

Trump also accused Maduro's government of using "stolen" oil to "finance themselves, Drug Terrorism, Human Trafficking, Murder, and Kidnapping".

The president has repeatedly accused Venezuela of drug smuggling. Since September, the US military has killed at least 90 people with its strikes on boats that were allegedly carrying fentanyl and other illegal drugs to the US.

However, it has provided no public evidence that these vessels were carrying drugs, be it fentanyl, which is mainly produced in Mexico, or cocaine.

Tuesday's post from Trump suggested that a label the US had previously applied only to Maduro was now being widened to his whole government.

Last month, the US formally alleged that the Venezuelan Cartel de los Soles group was an FTO. The designation meant that Maduro was effectively designated as a terrorist as well, because he was alleged to be the group's leader, which he denies.

In response to the recent US actions, Venezuela - home to the world's largest proven oil reserves - has accused Washington of seeking to steal its resources.

Venezuela's economy is heavily dependent on oil exports, even though the amount of oil it actually produces is relatively small given that the country is home to the world's largest proven reserves.

When announcing the tanker seizure off Venezuela's coast last week, the White House said the vessel in question, called the Skipper, had been involved in "illicit oil shipping" and would be taken to a US port.

Venezuela's government decried the move, with Maduro saying the US "kidnapped the crew" and "stole" the ship.

The US had been building up its military presence in the Caribbean Sea, which borders Venezuela to the north, in the weeks and months before the raid.

The build-up has involved thousands of troops and the USS Gerald Ford – the world's largest aircraft carrier – being positioned within striking distance of Venezuela.

Congressman Joaquin Castro, a Democrat representing Texas, said Trump's "naval blockade is unquestionably an act of war".

He added that US lawmakers would on Thursday vote on a resolution "directing the president to end hostilities with Venezuela".

The US, under both Trump and former President Joe Biden, has opposed the Maduro government for years and pressed for him to be removed by imposing stringent sanctions.

Maduro's government has been accused of rights abuses by the wider international community for many years. Venezuela's opposition, as well as many nations including the US, denounced last year's election as rigged and say his rule is therefore illegitimate.

On Tuesday, the UN human rights chief, Volker Türk, warned that the country's "crackdown on civic space has intensified, suffocating people's freedoms".