WASHINGTON (AP) — The United States on Friday added two companies involved in shipping oil from Venezuela to Cuba, along with nearly three dozen ships, to a financial sanctions list aimed at increasing pressure on Venezuelan President Nicolas Maduro to step down and turn over power to the opposition.

A Treasury Department statement announcing the designation identified one of the companies as Ballito Bay Shipping Inc., based in Monrovia, Liberia. It is the registered owner of the Despina Andrianna, which has been used in recent weeks to ship Venezuelan crude to Cuba.

The other company is ProPer Management Inc., which is based in Greece and is the operator of the Despina Andrianna, Treasury said.

Cuba is a major importer of crude oil from Venezuela and, in exchange, sends political advisers, intelligence and military officials and medical professionals who help the Maduro government stay in power, Treasury said.

Treasury’s action prohibits any U.S. citizen or entity from transactions involving the companies, which is intended to reduce their access to the global financial system.

Treasury also listed 34 ships that it said are assets of the Venezuelan state-owned oil company known by its initials as PdVSA.

The U.S. and about 50 other countries say Maduro’s re-election last year was not legitimate and have recognized the head of the National Assembly as the interim president of Venezuela.

The U.S. imposed sanctions on Venezuela’s oil industry in January to cut off the government’s most important source of revenue.