President Donald Trump announced Tuesday what he called a “blockade” of sanctioned Venezuelan oil tankers, ratcheting up American pressure on the regime of Venezuelan President Nicolas Maduro. 

“Venezuela is completely surrounded by the largest Armada ever assembled in the History of South America,” Trump wrote in a lengthy post on his social media platform. “It will only get bigger, and the shock to them will be like nothing they have ever seen before — Until such time as they return to the United States of America all of the Oil, Land, and other Assets that they previously stole from us.”

It was not immediately clear what stolen oil and land Trump was referring to. However, under Maduro’s predecessor, Hugo Chavez, the Venezuelan government expropriated assets from some American oil companies after the country nationalized oil fields in 2007. 

In the post, Trump announced “A TOTAL AND COMPLETE BLOCKADE OF ALL SANCTIONED OIL TANKERS going into, and out of, Venezuela” and demanded the return of oil and assets. 

The Venezuelan government responded to Trump’s post, calling his declaration a “reckless and serious threat,” against the country that it says violates international law, free trade and freedom of navigation.

“The President of the United States intends to impose in an absolutely irrational manner, a supposed naval military blockade on Venezuela with the objective of stealing the wealth that belongs to our homeland,” the Venezuelan government said in a statement.

The U.S. currently has 11 warships in the Caribbean — the most in decades — but even with a stepped-up presence, that would likely not be enough to put in place a blockade in the traditional sense, which involves sealing a country’s coastline completely.

Reuters reported last week the fleet of sanctioned ships helping move Venezuelan oil numbered about 30. According to Tanker Trackers, there are more than a dozen sanctioned tankers in Venezuelan waters at the moment.

Last week, the U.S. seized a sanctioned oil tanker off the coast of Venezuela that officials said was involved in an illicit oil shipping network supporting foreign terrorist organizations and used to transport oil between the South American country and Iran. The oil tanker was headed to Cuba.

Separately, since September, the U.S. military has launched dozens of strikes on vessels allegedly carrying drugs — moves the Trump administration has said are about stopping the flow of drugs into the U.S.  

Trump’s post Tuesday evening came after White House Chief of Staff Susie Wiles was quoted in Vanity Fair as saying that Trump “wants to keep on blowing boats up until Maduro cries uncle.”

In the post on Tuesday, Trump denounced Maduro’s government as a “Hostile Regime.”

While the U.S. has long considered Maduro the head of a corrupt dictatorial regime, Trump last month, in an unprecedented move, declared him the head of a foreign terrorist organization. 

“The illegitimate Maduro Regime is using Oil from these stolen Oil Fields to finance themselves, Drug Terrorism, Human Trafficking, Murder, and Kidnapping,” Trump wrote in the post on Tuesday. “For the theft of our Assets, and many other reasons, including Terrorism, Drug Smuggling, and Human Trafficking, the Venezuelan Regime has been designated a FOREIGN TERRORIST ORGANIZATION.”