The UK is due to outline a response later (Monday) to the seizure of a British-flagged oil tanker by Iran.
Tehran insists 'prudence and foresight' are necessary to de-escalate tensions.
The Stena Impero oil tanker was seized on Friday in the Strait of Hormuz, accused by Iran of violating international maritime rules.
It follows the seizure of an Iranian vessel off Gibraltar two weeks ago.
Olly Barratt reports from London.
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