Britain insists its oil tanker seized by Iran was in Omani territorial waters.
And it has called for the vessel to be released in a letter to the United Nations Security Council, accusing Iran of "illegal interference".
Oman has also urged Iran to let the tanker go.
This comes after the British government summoned Tehran’s top diplomat in London.
Al Jazeera's Nadim Baba joins us live from London, while Dorsa Jabbari reports from Tehran.