The 15 Royal Navy personnel seized at gunpoint in the Gulf by Iran are reportedly being questioned in Tehran.
Iranian armed forces spokesman Gen Ali Reza Afshar told Iranian radio the crew were being interrogated and had admitted being in Iranian waters.
He also said they were in "sterling health" and there had been no problems.
The British government says the eight sailors and seven marines were in Iraqi waters. It has demanded their immediate release.
The Fars news agency says the group - including one woman - was flown to Iran's capital and arrived in the Iranian capital at 1200 local time (0830 GMT).
Satellite tracking systems on the British boats proved they were inside Iranian waters, it added.
The German presidency of the European Union has demanded the immediate release of the personnel.
And Foreign Office junior minister Lord Triesman has met Iran's ambassador to London to demand their release.
The 15 were seized on Friday after boarding a boat in the Gulf.
They were from HMS Cornwall, based in Plymouth - the flagship of the coalition-Iraqi force which patrols Iraqi territorial waters in the northern Gulf to combat smuggling.
The Cornwall's commander, Commodore Nick Lambert, said they had been inspecting an Iraqi boat before clearing its skipper to continue with his business.
The personnel would have been in boats similar to those pictured
When they returned to their two small boats, they were "promptly arrested".
The helicopter then saw the British boats being moved along the Shatt al-Arab waterway to Iranian bases, Cmdr Lambert said.
There had been no evidence of fighting, he added.
Diplomats have held talks in Tehran and London since Friday's incident.
Ibrahim Rahimpour, Iran's director general for Western European affairs, said he had met the UK's charge d'affaires, Kate Smith, in Tehran.
He said he had delivered a "firm protest from Iran against the illegal entry of British sailors into Iranian territorial waters".
But former Royal Navy head Adm Sir Alan West dismissed suggestions the British boats had strayed into Iranian waters.
Sir Alan was first sea lord in 2004 when Iran detained eight British servicemen for three days after they allegedly strayed over the maritime border.
The men were paraded blindfolded and made to apologise on Iranian TV before their release was agreed.
Sir Alan told BBC News that tracking systems then had proven that the servicemen had been in Iraqi waters.
"They can do lots of smokescreens and things like that but I am absolutely clear in my mind it would have been in our waters," he said.
The Ministry of Defence has been in contact with relatives of the group.
Because of a long holiday period in Iran there has been little public comment.
The US military said it had been monitoring Iran's Revolutionary Guards - an elite fighting force appointed by the country's supreme leader, Ayatollah Ali Khamenei - "for years now" in Iraqi territorial waters.
BBC world affairs correspondent, Ian Pannell, who was earlier on board HMS Cornwall, said the mood on the ship was "quiet and determined" and that "the aspiration here is that this will be over sooner rather than later".
And the BBC's Bridget Kendall said the big question was whether the capture was part of a bigger political game, ahead of a UN Security Council vote in New York over further sanctions against Iran's nuclear programme.
But Sadegh Ziba Kalam, professor of politics at Tehran University, dismissed the idea that the seizure was a political move ahead of the vote.
"Everyone knows that would not change anything," he told BBC Radio 4's Today programme.
The seizure also follows claims that much of the violence against UK forces in Basra is being engineered by Iranian elements, which Tehran denies.