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 program 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, detained on November 25, 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.

British Foreign Secretary David Miliband held talks with Iranian Foreign Minister Manouchehr Mottaki late on Tuesday and he repeated his call for formal consular access to the men and their speedy release.

“He (Miliband) pressed Mr Mottaki for clear information on what had happened and for a statement of Iranian intentions in respect of the five,” a Foreign Office spokesman said in a statement.

It added that Mottaki undertook to get a response “at the earliest possible opportunity”.

Ahmadinejad gave an extended interview to Iran’s state television on Tuesday but made no mention of the Britons.

Earlier, Miliband told parliament he saw no political dimension to the case and 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,” he said.

PROPELLER FAULT

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

Andrew Pindar, chairman of Sail Bahrain, which owns the yacht, told reporters the crew believed they were in the waters of the United Arab Emirates.

“But due to a fault with a propeller they may have inadvertently drifted into Iranian waters.”

He said the crew appeared to be in good spirits and were being well looked after.

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.

The yacht that was crewed by five Britons when they were detained by Iranian officials is seen in this undated handout image received in London on December 1, 2009. REUTERS/Team Pindar/Handout

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 Britain’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.

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. (Additional reporting by Ramin Mostafavi, Parisa Hafezi in Tehran, Frederik Richter in Bahrain and Avril Ormsby and Stefano Ambrogi in London; Writing by Jon Hemming; Editing by Andrew Dobbie)