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 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.
"This sale of oil to (Syrian President Bashar al-Assad's) brutal regime is part of a pattern of behaviour by the Government of Iran designed to disrupt regional security."
Britain said it would raise the issue at the United Nations later this month.
(Reporting by William James, editing by Elizabeth Piper)