Britain declared on Monday that if Iran wanted to be accepted in the international community, then it needed to “come out of the dark” and release a British-flagged vessel it had seized in the Arabian Gulf.
"If the Iranians want to come out of the dark and be accepted as a responsible member of the intentional community they need to adhere to rules-based system of the international community," Foreign Secretary Dominic Raab told Sky News.
"You cannot go about detaining unlawfully foreign vessels."
Iranian commandos seized the tanker in the Hormuz Strait, the world's most important waterway for oil shipments, two weeks after British forces captured an Iranian oil tanker near Gibraltar, accused of violating sanctions on Syria.
Raab rejected the idea that London could release the Iranian tanker in exchange for the Stena Impero.
"There is no quid pro quo," he told BBC radio. "This is not about some kind of barter. This is about the international law and the rules of the international legal system being upheld and that is what we will insist on."
His remarks coincided with Iran’s Revolutionary Guards releasing on Monday of footage purportedly showing the Guards warning off a British warship during their July 19 seizure of the Stena Impero.
The video, published by the semi-official Tasnim news agency, contains footage of the capture of the tanker, showing Guards abseiling onto the deck from a helicopter, with the audio recording superimposed.
"You are required not to interfere in these issues," the Guards' navy representative says.
"This is British warship foxtrot two three six. I am in the vicinity of an internationally recognized strait with a merchant vessel in my vicinity conducting transit passage," a voice with a British accent replies.
"Don't put your life in danger," the Guards navy representative says.
The video also contains an exchange between the Guards and the same British warship during a stand-off in mid-July involving the British Heritage oil tanker, according to Tasnim.
Three Iranian vessels attempted to block the passage of a ship, the British Heritage, through the Strait of Hormuz, but withdrew after warnings from a British warship, the British government said on July 11.
Britain last week started sending a warship to accompany all British-flagged vessels through the Strait of Hormuz, a change in policy announced on Thursday after the government previously said it did not have resources to do so.
