Iran says may take serious action against Britons

By Hossein Jaseb and Keith Weir

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 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.

Oil prices rose by over $1 on fears of a diplomatic crisis shortly after news of the detainment was made public on Monday.

"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 a 2007 incident when Iran seized eight Royal Navy sailors and seven marines off its coast.

"There is certainly no confrontation or argument. As far as we are aware these people are being well treated, which is right, and what we would expect from a country like Iran," Foreign Secretary David Miliband BBC Radio 4.

Miliband said he was expecting a statement later on Tuesday from the Iranian Foreign Ministry.

"We understand that the Iranian government are investigating the incident, which is perfectly reasonable, and then we would look forward to it being promptly sorted out," Miliband said.