WASHINGTON, June 13 (Reuters) - An unexploded device, believed to be a limpet mine, was spotted on the side of one of two oil tankers attacked on Thursday in the Gulf of Oman, a U.S. official told Reuters, speaking on condition of anonymity.

If confirmed, then the method of attack would be the same as the one that the United States believes was used last month when four other tankers were struck off the coast of the United Arab Emirates. The United States believes Iran was likely responsible for those attacks, a charge Tehran denies. (Reporting by Phil Stewart Editing by James Dalgleish)

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