Two vessels have reported suspicious approaches by a skiff in the Gulf of Aden on Thursday.
Security consultancy Ambrey reported that the ships spotted a boat when they left the Bab el Mandeb Strait.
The first incident took place at 0804 GMT and is reported to have involved a Hong Kong-flagged LPG carrier eastbound at 13.5 knots.
The skiff was making 19 knots.
"The embarked security team responded with several warning shots and the skiff distanced itself from the immediate area. Vessel and crew are safe," Ambrey said.
A short time later, 12 nautical miles (22 km) ahead of the first incident, a Panama-flagged MR tanker also reported an encounter.
Regional authorities are currently investigating both, but an initial assessment has indicated that there was no hostile intent or capability displayed by occupants of the skiffs involved, Ambrey added.
Another security consultant, Dryad Global, said the gas carrier had been approached 55 nautical miles south-west of Aden.
The firm has cited intelligence claiming there were up to six boats in the area, but it is unclear how many approached the ship.
No weapons or ladders were reported.
This latest incident is the eight recorded approach within the maritime security transit corridor in 2020 and the fourth near the southern Bab el Mandeb.
Incidents have thus far all been recorded as suspicious approaches.
This is a doubling of all incidents logged at the same point last year.
No increase in security threat
"Despite this there remains little evidence to suggest a significant increase in the maritime security threat art this stage," Dryad said.
"There are currently no incidences of vessels undergoing persistent approach, or shots being fired at vessels and other key indicators of piracy intent."
At the start of March a raid on a product tanker by armed attackers was thwarted by a warship in the Gulf of Oman.
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.
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".
Other incidents took place further south in the Gulf of Aden off Yemen and Somalia.
Another involved the 19,800-dwt Aurora Tankers product carrier Wawasan Emerald (built 2010) in February.
The Panama-flagged vessel was passing through the maritime security transit corridor at the time, about 40 km south of Yemen.
Pirate boats approached to within 0.5 nautical miles (0.9 km) of the handysize tanker.
