Iran has released five Britons who had been detained in the Gulf after their yacht apparently strayed into Iranian waters, state radio said.

British Foreign Secretary David Miliband held talks with Iranian Foreign Minister Manouchehr Mottaki late on Tuesday and called for formal consular access to the men and their speedy release. They were detained on Nov. 25.

"After getting necessary guarantees, Iran released the five," state radio quoted a statement issued by the Revolutionary Guards.

"We reached the conclusion that they entered Iran's territorial waters by mistake."

A senior official said on Tuesday that Iran would take serious measures against the five yachtsmen if it proved they had "evil intentions".

Relations between Britain and Iran have been dogged by tension in recent years over a range of issues, from Tehran's nuclear programme to Iranian allegations of British involvement in post-election violence in June this year.

Britain stressed the five men were civilians and played down parallels with an incident in March 2007 when Iran seized eight British Royal Navy sailors and seven marines off its coast.