The United States has seized an oil tanker off the coast of Venezuela in international waters, according to officials quoted by international news agencies.

The incident occurred on Saturday, just days after US President Donald Trump announced a blockade of all sanctioned oil tankers entering and leaving Venezuela.

This is the second time in recent weeks that the US has seized a tanker near Venezuela, and it comes amid a large US military buildup in the region as Trump continues to ramp up pressure on Venezuelan President Nicolas Maduro.

Three officials, speaking to the Reuters news agency on condition of anonymity, did not disclose the location of the operation but noted that the coastguard was in the lead.

Two officials, speaking to The Associated Press news agency, also confirmed the operation. The action was described as a “consented boarding”, with the tanker stopping voluntarily and allowing US forces to board it, one official said.

Reporting from Washington, DC, Al Jazeera’s Heide Zhou-Castro said that there was no official confirmation from US authorities on the incident.

“We are still waiting for confirmation from the White House and Pentagon on the details, including which ship, where it was located, and whether or not this ship was beneath the US sanctions,” she said.

Sharp fall in exports

In the days since US forces seized a sanctioned oil tanker off Venezuela’s coast last week, there has been an effective embargo in place, with loaded vessels carrying millions of barrels of oil staying in Venezuelan waters rather than risking seizure.

Since the first seizure, Venezuelan crude exports have fallen sharply.

While many vessels picking up oil in Venezuela are under sanctions, others transporting the country’s oil and crude from Iran and Russia have not been sanctioned. Some companies, particularly the US’s Chevron, transport Venezuelan oil in their own authorised ships.

China is the biggest buyer of Venezuelan crude, which accounts for about 4 percent of its imports, with shipments in December on track to average more than 600,000 barrels per day, analysts have said.

For now, the oil market is well supplied, and there are millions of barrels of oil on tankers off the coast of China waiting to offload.

If the embargo stays in place for some time, then the loss of nearly a million barrels a day of crude supply is likely to push oil prices higher.

Trump’s pressure campaign on Maduro has included a ramped-up military presence in the region and more than two dozen military strikes on vessels in the Pacific Ocean and Caribbean Sea near Venezuela, which have killed at least 100 people.

Trump has also said that US land strikes on the South American country will soon start.

Maduro has alleged that the US military buildup is aimed at overthrowing him and gaining control of Venezuela’s oil resources, which are the world’s largest crude reserves.

On Saturday, Brazilian President Luiz Inacio Lula da Silva warned Trump against an “armed intervention in Venezuela”, saying that it “would be a humanitarian catastrophe”.

At a summit of the South American Mercosur bloc in Foz do Iguacu, a city in southern Brazil, Lula repeated his stance against the US’s actions towards Venezuela in a stronger statement, stressing that it would be a “dangerous precedent for the world”.

More than four decades after the Falklands War, between Argentina and the United Kingdom, he added, “The South American continent is once again haunted by the military presence of an extra-regional power.”