Iranian television on 1 April showed pictures of two of the 15 British sailors and marines held in Iran, the men saying they were captured after entering Iranian waters.
Britain had earlier said it was in direct communication with Iran as it seeks the release of the 14 men and one woman detained on March 23 in the northern Gulf.
Iran’s capture of the Britons has drawn international criticism, but Tehran has so far ignored calls to release them.
The row, at a time of heightened Middle East tensions over Tehran’s disputed nuclear programme, pushed oil prices last week to six-month highs. The West accuses Iran of trying to build nuclear bombs, a charge Tehran denies.
State-run Al-Alam television showed footage of the two men in khaki uniforms standing separately in front of a large map of the Gulf, and pointing to it while speaking.
The map showed the positions of various vessels near the mouth of the Shatt al-Arab waterway, which forms the southern border between Iran and Iraq. Written on the map in English was “the point where intruding boats were captured”.
“At approximately about 10 o’clock in the morning we were seized, apparently at this point here from their maps and the GPS they showed us, which is inside Iranian territorial waters,” Captain Chris Air said in the footage which was released to international broadcasters.
“So far we have been treated very well by all the people here. They have looked after us and made sure that ... (they) feed us enough food and we’ve been treated very well from them so we thank you for that.”
The second Briton said: “My name is Lieutenant Felix Carmen ...Yes, I’d like to say to the Iranian people, I can understand why you were so angry about our intrusion into your waters ... ”
In London, a Foreign Office spokeswoman said: “I would just reiterate that it’s unacceptable for these pictures to be shown given the potential distress to their families.”
“There is no doubt where our personnel were. They were in Iraqi territorial waters.”
Footage of a British sailor apologising for entering Iranian waters was broadcast on Friday. It was not clear when the footage shown on Sunday was filmed.
British Defence Secretary Des Browne earlier said diplomatic efforts were continuing to resolve the crisis.
“We are anxious that this matter be resolved as quickly as possible and that it be resolved by diplomatic means and we are bending every single effort to that,” Browne told BBC television.
“It’s not my intention to go through the detail of that blow by blow, and it wouldn’t be appropriate to do that, but we are in direct bilateral communication with the Iranians,” he said.
The Foreign Office spokeswoman said Britain had not had any diplomatic contact with the Iranians on Sunday and was awaiting a response to the diplomatic note it sent to Iran.
In Tehran, about 200 demonstrators chanted: “British, British, death to you, death to you” at Britain’s embassy.
Protesters threw firecrackers into the embassy compound. No one was hurt by the small explosive devices, which went off with loud bangs and sent clouds of smoke rising into the air.
U.S. President George W. Bush on Saturday called on Iran to release the 15 at once. “The Iranians must give back the hostages. They’re innocent,” he said. “The Iranians took these people out of Iraqi waters. It’s inexcusable behaviour.”
Bush’s use of the term “hostages” evoked the storming of the U.S. embassy in Tehran after the 1979 Islamic revolution and the holding of 52 Americans for 444 days. Washington broke off relations as a result.
Responding to Bush’s comments, Iranian Foreign Ministry spokesman Mohammad Ali Hosseini said the United States could damage the British cause, the Iranian state TV Web site said.
“Any comments by Americans in support of the British government could make the situation worse, therefore it is better if the American president does not make non-technical, ill-considered and illogical comments,” Hosseini said.