Vietnam’s state oil company urged the US to let a supertanker pass through an American naval blockade outside the Persian Gulf, saying the shipment is critical to the Asian country’s economy.

The very large crude carrier Agios Fanourios I, managed by Athens-based Eastern Mediterranean Maritime, performed a mid-ocean U-turn on Monday at around the point where the US blockade begins. It had only just cleared the Strait of Hormuz, holding 1.99 million barrels of Iraq’s Basrah Medium crude, when it turned back, according to ship tracking and paperwork.

PetroVietnam Oil, the trading arm of the state energy company, confirmed to US Naval Forces Central Command that it owned the cargo on the Agios Fanourios I and that it was loaded in Iraq, according to a letter. The vessel is still signalling its destination as Nghi Son, home to a refinery in the Asian country.

“This cargo is of extreme importance to Nghi Son Refinery, to the Socialist Republic of Vietnam and to the Vietnamese people,” the letter said. “Any further delay risks halting refinery throughput, with cascading consequences for millions of Vietnamese consumers, businesses, public services and industries.”

The struggle to get barrels out shows how the US blockade has further complicated what was already an almost-impossible task for tanker owners trying to export oil from the region during the war. Saudi Aramco’s CEO said this week that 100 million barrels a week of supply are being lost.

US Central Command said the navy turned the vessel around “to enforce the blockade against Iran which is meant to prevent transit by any vessels going to or from Iranian ports”.