The 15 British navy personnel detained in the Gulf have been transferred to Tehran to explain their "aggressive action," according to reports.

Efforts are continuing to secure the release of the 15 Royal Navy sailors and Royal Marines seized by Iranian patrol boats off the coast of Iraq.

Britain has been plunged into a potentially dangerous new diplomatic crisis after the boarding party was seized at gunpoint on Friday.

On Saturday, a senior Irainian commander claimed the group had admitted they were in Iranian waters, but the British Foreign Secretary Margaret Beckett was adamant they were in Iraqi waters at the time.

She said she was "extremely disturbed" they had been detained in Tehran.

Tehran's ambassador to London was summoned to the Foreign Office at her instruction to be told by a senior official they should be released immediately.

And after the 20-minute meeting - described by Mrs Beckett as "brisk and polite" - it emerged that Tehran had also called in British diplomats for talks.

An unnamed foreign ministry official was quoted by state television accusing the sailors and Marines of a "blatant aggression into Iranian territorial waters".

The developments coincide with UN deliberations over possible sanctions against Iran over its refusal to abandon work on producing enriched uranium needed to build a bomb.

The naval boarding party, from the Type 22 frigate HMS Cornwall, was taken at gunpoint by the Iranians after carrying out a routine search of a large cargo dhow which they suspected of smuggling in the northern Persian Gulf.

The group of eight sailors and seven Marines is believed to include at least one woman.

HMS Cornwall is currently the flagship of the joint coalition-Iraqi Combined Task Force 158 responsible for patrolling Iraqi territorial waters in the northern Gulf.

The task force commander, Commodore Nick Lambert, said he hoped the incident was the result of a "misunderstanding" which could be quickly resolved.

The seizure of the boarding party carries echoes of an incident in June 2004 when a party of eight Marines and sailors were held for three days after being seized by the Iranians in the Shatt al-Arab.