“After the US recognised Juan Guaido as the interim president of Venezuela and put full-on sanctions on PDVSA, the Maduro regime would not let the tanker leave its waters,” said Russ Dalen, from Miami-based Caracas Capital in a note to investors on February 13.

“We reached out to Citgo at the highest levels for confirmation of whether the Gerd was offloading by agreement or by force,” said Mr Dallen, adding that the company did not want to comment.

Shipments tracked in January reached 930,000 bpd in January, according to Lloyd’s List Intelligence data, less than half volumes seen two years ago. Russian oil company Rosneft is selling much of the oil and charters about 80% of tankers exporting from Venezuela, according to Mr Dallen. India and China are now the biggest buyers, after restrictions on sales to the US sidelined Venezuela from its biggest market.