Iran accuses Britain over sailors
HMS Cornwall
Commodore reacts
Fifteen British navy personnel captured at gunpoint by Iranian forces had sailed into Iran's waters illegally, its government has insisted.
An Iranian official said Tehran had made a "firm protest" about the "illegal entry" in the Gulf.
The UK maintains the eight sailors and seven marines had been carrying out routine duties in Iraqi waters.
The personnel, who are thought to be unharmed, were seized at 1030 local time after boarding a boat in the Gulf.
Iranian and UK diplomats have met in Tehran and London in the wake of the 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.
HMS CORNWALL FACTS
Multi-national force flagship in the northern Gulf
Type 22 frigate
Crew: 250 (Max 301)
Length: 148.1m / 485.9ft
Speed: 30 knots
Source: Royal Navy
Profile of HMS Cornwall
Ex-detainee 'concerned'
Tense backdrop to incident
He said in a statement that he had delivered a "firm protest from Iran against the illegal entry of British sailors into Iranian territorial waters".
The statement added: "They were arrested by border guards for investigation and questioning."
Mr Rahimpour accused British sailors of having illegally entered Iranian waters "a number of times".
Both the Royal Navy and UK Foreign Secretary Margaret Beckett denied the navy personnel from HMS Cornwall, which has its home port in Plymouth, had sailed into Iranian waters.
Mrs Beckett demanded their immediate and safe return.
HMS Cornwall's area of operations
Mrs Beckett said: "We understand that they were in two boats that were operating in Iraqi waters in accordance with the Security Council Resolution 1723 in support of the government of Iraq to stop smuggling."
Royal Marines on waterways in the Basra
Servicemen would have been in boats similar to those pictured
She said Iran's ambassador to the UK, Rasoul Movahedian, had met Foreign Office officials for a "brisk but polite" discussion on Friday afternoon.
Commodore Nick Lambert said he had "absolutely no doubt" the vessel had been in Iraqi waters, adding that it could be "a simple misunderstanding at the tactical level".
This was supported by US military monitoring the movement of Iran's Revolutionary Guards.
US Navy spokesman Commander Kevin Aandahl told the BBC: "They were in Iraqi territorial waters.
"We have been operating in those waters for years now. We know what the territorial lines are, we respect those territorial lines and we expect the Iranians to respect those territorial lines as well."
The incident comes at a time of renewed tensions with Iran over its nuclear programme.
It also follows claims that much of the violence against UK forces in Basra is being engineered by Iranian elements, which Tehran denies.
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BBC world affairs correspondent, Ian Pannell, who is on board HMS Cornwall, said the mood on the ship was "quiet and determined" and that everybody had rallied together.
"The aspiration here is that this will be over sooner rather than later," he said.
"I think certainly the hope of the commanding officers is the events which have taken place here are possibly some kind of accident.
"Certainly they're hoping in the next 24 to 48 hours to get some positive news."
In 2004, Iran detained eight British servicemen for three days after they allegedly strayed over the maritime border.
The UK claimed the men were "forcibly escorted" into Iranian territorial waters.
The men were paraded blindfolded and made to apologise on Iranian TV before their release was agreed.