Tehran: Iran has warned that it will take strong action against five detained British sailors if it is proven they had "bad intentions" after the Iranian navy stopped their racing yacht in the Gulf.

The detention could heighten tensions between Iran and major world powers, including Britain, that are demanding a halt to Tehran's controversial nuclear program. It could also flare up the longtime rivalry between Iran and Bahrain, since the yacht was the pride of a high-profile racing programme sponsored by the Arab Gulf nation's king.

British Foreign Secretary David Miliband said "there is certainly no question of any malicious intent on the part of these five young people."

Britain says the yacht, called Kingdom of Bahrain, strayed inadvertently into Iranian waters while en route to a race off Dubai.