"We are aware of reports of an attack on a merchant vessel off the coast of Oman," the Ministry of Defence in London said in a short statement.

"UK military headquarters in the region are currently conducting investigations."

The United Kingdom Maritime Trade Operations (UKMTO) -- an anti-piracy taskforce run by the Royal Navy -- issued a report of "a vessel being attacked" around 152 nautical miles (280 kilometres) off the coast of Oman.

Shipping firm Zodiac Maritime said it was "a suspected piracy incident" involving the tanker Mercer Street, a Japanese-owned vessel managed by London-based Zodiac.

"At the time of the incident the vessel was in the northern Indian Ocean, travelling from Dar es Salaam to Fujairah with no cargo on board," it added.

"We are in coordination and liaising with the UKMTO and other relevant authorities."

Zodiac Maritime is part of the Zodiac Group, owned by Israeli businessman Eyal Ofer, whose enterprises span shipping, real estate, technology, banking and investments.

Ofer was ranked the world's 197th richest person by Forbes this year, with a fortune of $11.3 billion. His firms own and operate over 160 ships.

The Arabian Sea and surrounding Indian Ocean were plagued by piracy around a decade ago, but incidents have waned in recent years after foreign navies stepped up patrols.