The photo has been used for illustrative purposes.

Two crew members of an oil tanker linked to an Israeli billionaire were killed off Oman in the Arabian Sea, authorities said on Friday.

They were the first fatalities after years of assaults targeting shipping in the region as the assault represented the worst-known maritime violence so far.

US and European sources familiar with intelligence reporting said on Friday that Iran is the leading suspect in an attack on an Israeli-managed petroleum products tanker off Oman but it is too early to say for sure.

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US Navy forces came to the aid of the crew in response to an emergency distress call and saw evidence of the attack, said an American military statement.

It added that initial indications "clearly point" to a drone-style attack, and that US Navy ships were now escorting the vessel with US personnel aboard to help.

Separately, a US defense official said the Mercer Street, a Liberian-flagged, Japanese-owned ship managed by Israeli-owned Zodiac Maritime, appeared to have been attacked by a drone, or unmanned aerial vehicle.

While no one has claimed responsibility for the attack Israeli officials also alleged Tehran launched the drone strike.

The strike on Thursday night on the oil tanker Mercer Street marks the first-known fatal attack after years of assaults on commercial shipping in the region linked to tensions with Iran over its tattered nuclear deal.

While Iran did not directly acknowledge the attack, the strike comes as Tehran now appears poised to take an even tougher approach with the West as the country prepares to inaugurate a hard-line protégé of Supreme Leader Ayatollah Ali Khamenei as president.

No one immediately claimed responsibility for the Thursday night raid on the Liberian-flagged tanker Mercer Street.