Eight British servicemen captured by Iran after their boats supposedly strayed into Iranian waters were "forcibly escorted" across the national boundary from Iraq, Britain's defence minister said on Wednesday.
The six marines and two navy sailors were detained for three days in Iran last week, during which they were paraded blindfold on television and forced to publicly apologise for what they called a "mistake".
Iran insisted that the boats were intercepted only after they entered Iranian waters on the Shatt al-Arab waterway that divides southern Iraq from Iran.
But in a strongly-worded written statement, British Defence Secretary Geoff Hoon dismissed this version of events.
"In a recent debriefing the crews have said that they were operating inside the Iraqi border and were forcibly escorted into Iranian territorial waters," he said.
"Our assessment continues and will be greatly assisted by the retrieval of navigational information in the Global Positioning System equipment carried by the crews," he said.
This equipment, along with the three boats in which the servicemen had been travelling, had yet to be returned by Iran despite a deadline set by Britain of Tuesday, Hoon said.
He continued: "We are very concerned about the blindfolding of the men and have made representations to the government of Iran.
"We have made it clear that we do not expect a recurrence of this incident."
British forces were issued with up-to-date charts and equipment which meant it was unlikely they would have misjudged the border, the statement added.
The eight servicemen were released on Friday, and although the men were not harmed, their detention and public display angered London and threatened to derail relations between the countries.
It came amid a more general downturn in ties, with Britain co-sponsoring a resolution passed by the International Atomic Energy Agency earlier this month that heavily criticised Iran for failing to cooperate fully with an investigation into its nuclear programme.
Earlier Wednesday, a leading British defence publication said that British forces had almost launched major combat operations against Iranian troops who had encroached over the southeastern Iraqi border in July last year.
A US general asked British forces to "prepare plans for offensive operations" after Iranian troops moved across the border near the Iraqi city of Basra, an article in Defence Analysis magazine said.
"Eventually diplomatic negotiations managed to achieve a pull-back of Iranian forces, so offensive use of British troops was not needed," it said.