TEHRAN (AFP) –
Iran said on Tuesday that five British sailors detained in southern Gulf waters by the elite Revolutionary Guards would be dealt with firmly if found guilty of what it called "ill intentions."

The five men on board an 18-metre (60-foot) racing yacht were detained last week by the Revolutionary Guards, the force's navy chief told the Fars news agency.

President Mahmoud Ahmadinejad's chief of staff, Esfandiar Rahim Mashaie, said the way to deal with the Britons "arrested in the Persian Gulf by Iranian forces will be decided by the judiciary," Fars reported.

"If these people's ill-intention is proven, they will be dealt with seriously and firmly," he said, adding that Tehran had in the past dealt firmly with people who "entered Iran illegally."

Reacting to Mashaie's comments, British Foreign Secretary David Miliband said "there's certainly no question of any evil intent," insisting that the five were clearly innocent and saying that he hoped for a speedy resolution. Related article: Britons held in Iran 'tough', say families.

He also said the sailors' detention has "nothing to do" with politics or the stand-off over the Islamic republic's nuclear programme, which the West suspects has military aims despite Tehran's denial.

"This is a human story of five young yachtsmen," Miliband told reporters in London. "It's a consular case, which is being treated as a consular case by the UK, and I'm sure will be treated as a consular case by the Iranian authorities."

He said earlier on Tuesday that Britain has "no argument" with Tehran over the sailors and stressed that they were being treated well.

The seizure, which recalls the detention by Iran of 15 British navy personnel in the Gulf in 2007, comes amid already heightened tensions between Tehran and the West over Iran's nuclear plans.

The five were sailing from Bahrain to the start of a race in the emirate of Dubai when their yacht, "The Kingdom of Bahrain," was stopped last Wednesday in the Gulf, the Foreign Office said.

They are believed to have been intercepted near the Iranian-controlled island of Abu Musa, whose ownership is disputed by Iran and the United Arab Emirates, a Bahraini interior ministry source told AFP.

Miliband stressed that the latest incident was different from the one in 2007, which involved military personnel.

"It is important to say that these are civilians, not Royal Naval personnel," he said. "They are yachtsmen, they were going about their sport and it seems they may have strayed inadvertently into Iranian waters."

Revolutionary Guards navy chief Ali Reza Tangsiri told Fars that the Britons had been arrested by his forces.

"The British intruders have been arrested by the Guards' navy," he said, adding that "the movements in the Persian Gulf are under the supervision of Sepah (Guards)."

The yacht may have been drifted into Iranian waters after breaking its propeller en route to the Dubai-Muscat Offshore Sailing Race, which started last Thursday, British media reports said.

Informed sources in London have named the crew as Oliver Smith, Oliver Young, Sam Usher, Luke Porter and David Bloomer.

On a visit to Seoul, Iran's Nobel peace laureate Shirin Ebadi called for their release. "I believe the Iranian government has arrested them without warnings. They must be released as soon as possible," she told reporters.

Ebadi, a lawyer, said the Britons might have entered Iranian territorial waters by mistake. "In this case, maritime police should have escorted them out into international waters," she said through an interpreter.

Charles Porter said he had spoken to his 21-year-old son Luke on a mobile phone since the incident and that he appeared to be in good spirits.

"From what we understand there was an oilfield on their charts -- which is a restricted area -- so they chose to go one side of it," Porter said, adding the yacht may therefore have strayed too close to an Iranian island.

The Foreign Office said it could not say where the Britons were being held or if they were in prison.

In the 2007 incident, eight sailors and seven marines were captured on March 23. Britain insisted they were in Iraqi territorial waters, while Tehran said they were in Iranian waters. Related article: Other instances of Westerners detained in Iran.

During the 13 days they were held, the 14 men and one woman were not mistreated but they were paraded on Iranian television, sparking anger from Britain and other Western governments.