Britain summoned the Iranian ambassador on Tuesday to condemn what it said was a clear breach of the assurances it was given over the oil cargo of the tanker Adrian Darya 1, which had previously been detained at Gibraltar for breaching EU sanctions.
"Iran has shown complete disregard for its own assurances over Adrian Darya 1," foreign minister Dominic Raab said in a statement, accusing Iran of reneging on a promise not to transfer oil from the tanker to Syria.
Adrian Darya 1, formerly Grace 1 was seized by British Royal Marines on July 4 on suspicions of carrying oil for Syria in violation of EU sanctions. The tanker was released in August against appeals by the United States to extend the detention.
The protest is a reaction to an announcement by Iran on September 9 that the supertanker carrying two million barrels of oil has unloaded its cargo on the eastern Mediterranean coast.
Britain said it would raise the issue at the United Nations later this month.
"This sale of oil to (Syrian President Bashar al-Assad's) brutal regime is part of a pattern of behavior by the Government of Iran designed to disrupt regional security."
However, Tankertrackers.com tweeted later Monday that the Iranian tanker appears to be still loaded based on an analysis of satellite imagery.