TEHRAN/LONDON, (Reuters) – Iran will take serious measures against five British yachtsmen detained in the Gulf if it proves they had “evil intentions”, a close aide to Iranian President Mahmoud Ahmadinejad said on Tuesday.

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.

“The judiciary will decide about the five … naturally our measures will be hard and serious if we find out they had evil intentions,” Esfandiar Rahim-Mashaie, the president’s chief of staff, told the semi-official Fars news agency.

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.

“There is certainly no question of any malicious intent on the part of these five young people,” British Foreign Secretary David Miliband told BBC television.

Miliband later told parliament that he saw no political dimension to the case and that the men were being treated well. “I think it is important to say there is no link at all between the position of the yachtsmen and the Iranian nuclear file or other political issues that exist between Iran and the international community,” Miliband said.

Britain requested details on where the men were being held and access to them for consular officials in a meeting between a senior official and the Iranian ambassador in London on Tuesday.

Iran’s English-language state Press TV said the Britons were detained “kilometres away from their claimed route of Bahrain to Dubai. They were detained near the Iranian island of Siri,” Press TV said.

Hardline Iranian students will gather outside the British embassy in Tehran on Wednesday to protest against “the Britons’ illegal entry” into Iranian waters aboard the racing yacht Kingdom of Bahrain, the ISNA news agency reported.

Britain is often singled out for suspicion in the minds of many Iranians because of meddling during the colonial era.

Iranian Supreme Leader Ayatollah Ali Khamenei called Britain “the most treacherous” of Iran’s enemies after Prime Minister Gordon Brown condemned Tehran’s violent suppression of protests that followed the disputed June presidential election.

Iran’s reformist opposition is planning to hijack an official demonstration on Monday to keep up pressure on the hardline establishment. For Iran, the timing of capture of the sailors, may be fortuitous. “They are so convinced that the British are orchestrating all the problems within Iran … this will be just the sort of thing to keep the British press and the embassy in Tehran occupied,” said Ali Ansari of Scotland’s St. Andrews University. “What it will do is detract attention, Miliband has to be very nice and gentle,” Ansari said. “My feeling is they will keep the tension up until Monday has passed and then gradually it’ll start to ease, then they will probably release them.” Three Americans who crossed into Iran from Iraq in July are still detained and face spying charges. Their families say they were hiking and strayed across the border accidentally.

Iran’s Revolutionary Guards confirmed on Tuesday their naval forces had detained five Britons in the Gulf.

Miliband said the sailors may have “inadvertently strayed” into Iranian waters. Britain said their yacht, the Kingdom of Bahrain, was stopped by Iranian naval vessels on Nov. 25.

Organisers of a race in which the yachtsmen were planning to take part said the vessel had reported problems with a propeller en route from Bahrain to Dubai in the Gulf.

Gulf Arab state Bahrain, a partner of the yachting team for which the crew was racing, said on Tuesday it would help to resolve the crisis.

“The director of the consular department at the foreign ministry, Ambassador Yusuf Ahmed, is currently in touch with Iranian authorities to release the crew of the racing boat,” the official Bahrain News Agency said.