Iran, July 12 -- Iran on Friday demanded the British navy release an Iranian oil tanker seized last week off Gibraltar, accusing London of playing a "dangerous game" and threatening retribution, while London announced it was sending a destroyer to the Persian Gulf.

The comments from Iran's Foreign Ministry came the day after police in Gibraltar, a British overseas territory on the southern tip of Spain, said they arrested the captain and chief officer of the supertanker suspected of breaching European Union sanctions by carrying a shipment of Iranian crude oil to Syria.

Foreign Ministry spokesman Abbas Mousavi told Iranian state news agency IRNA that "the legal pretexts for the capture are not valid ... the release of the tanker is in a...