Four tankers whose cargoes were seized by the U.S. over the past month were heading to Venezuela with gasoline loaded in Iran, according to Iranian Oil Minister Bijan Namdar Zanganeh. His comments are the first acknowledgment by Tehran that the vessels were transporting shipments from the Islamic Republic when the U.S. confiscated them. Iran’s President Hassan Rouhani said on Saturday it was a “lie” that the tankers were Iranian, though he didn’t comment on what they held.

James Malloy, commander of the U.S. Fifth Fleet based in Bahrain, said on Monday that Washington used contracted vessels to seize the Iranian fuel and transfer it to other ships. Two of the transfers took place in the Gulf of Oman, and the other two occurred off the coast of Mozambique, he said on a call with reporters. The seizure was an unprecedented step by Washington, which said the ships contained 1.1 million barrels of gasoline, and it could destabilize global oil markets if Iran retaliates. The U.S. Navy is in contact with commercial shipping amid perceived Iranian threats, Malloy said.

Iran has the means to disrupt the flow of international tankers transiting the Strait of Hormuz, the world’s most critical chokepoint for oil shipments. However, the impact that such interference might have on oil prices would probably be limited, given that pandemic-driven lockdowns have battered demand for energy. Brent crude gained 0.4% to $45.19 a barrel by 3:28 p.m. in London on Monday, paring its loss this year to 32%.

“The cargoes were loaded from Iran, but neither the ships nor the cargoes belonged to Iran, and the U.S. declared victory for itself in the middle of this,” Zanganeh said earlier on Monday at a briefing in Tehran. “The fuel was Iranian, but it had been sold to Venezuela and its payment had been cleared.”

Malloy drew a sharp distinction between what he described as non-military seizures ordered by the U.S. and Iran’s forcible boarding of a smaller tanker, the Liberian-flagged Wila, on Aug. 12 in the Gulf of Oman.