President Donald Trump’s administration has seized an oil tanker off the coast of Venezuela, two U.S. officials told Reuters on Wednesday.

The move comes amid a massive U.S. military build-up in the region, including an aircraft carrier, fighter jets and tens of thousands of troops.

The officials, who were speaking on the condition of anonymity, said the operation was led by the U.S. Coast Guard. They did not name the tanker and did not say specifically where the interdiction took place.

The Coast Guard referred questions to the White House, which did not immediately respond to a request for comment. The Venezuelan government did not immediately respond to a request for comment.

Venezuela exported more than 900,000 barrels per day (bpd) of oil last month, the third-highest monthly average so far this year, as state-run company PDVSA imported more naphtha to dilute its extra heavy oil output. Even amid increasing pressure over Venezuelan President Nicolas Maduro, Washington had not moved to interfere with the country’s oil flows.

Oil exports are Venezuela’s main source of revenue. The country is struggling to sell its crude at full price in China, the main destination of its oil exports, due to growing competition with sanctioned oil from Russia and Iran.

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(Reporting by Idrees Ali and Phil Stewart, additional reporting by Jonathan Saul, editing by Chris Reese and Chizu Nomiyama)