A raid on a product tanker by armed attackers was thwarted by a warship in the Gulf of Oman on Sunday morning.
The incident was first reported by United Kingdom Maritime Trade Operations (UKMTO), which issued an advisory notice saying two skiffs had approached a vessel and proceeded to circle it.
A "coalition warship" was in the vicinity and approached, causing the boats to leave, the agency added.
The crew and vessel were reported safe at that time.
On Monday, security consultancy Ambrey upgraded the incident to a boarding.
Message relayed
An Ambrey security asset in the area relayed a VHF message between the Tanzania-flagged, 2,950-dwt Lady Sarah (built 1981) and the warship.
According to the transcript, the tanker had been "boarded" by "five armed personnel".
When the naval vessel approached, the gunmen "disembarked".
Ambrey said it had independently verified this was the master's original statement, but it understands this has since been retracted.
Operator Prime Tankers of Dubai could not immediately comment as management were in meetings on Monday.
There has been no AIS update from the vessel since last June.
The tanker has a clean port state control record dating back to 1999 and is classed by Intertek Maritime Bureau.
The spectre of a renewed piracy threat in the region has grown in the last two weeks, with three incidents of suspicious approaches by skiffs.
But these took place further south in the Gulf of Aden off Yemen and Somalia.
The latest incident involved the 19,800-dwt Aurora Tankers product carrier Wawasan Emerald (built 2010) last Tuesday.
The Panama-flagged vessel was passing through the maritime security transit corridor at the time, about 40km south of Yemen.
Pirate boats approached to within 0.5 nautical miles (0.9 km) of the handysize tanker.
