Contact has been lost with a bunker tanker in the Gulf of Guinea as the pirate threat remained critical in the region.
The incident comes as piracy reporting bodies also said a suspicious skiff approached a tanker owned by Norway's Kristian Gerhard Jebsen Skipsrederi (KGJS).
The last known position of the 400-dwt bunker ship Stelios K (built 1995) was 40 nautical miles (74 km) south of Lome in Togo on Monday morning.
The vessel was en route to Lagos in Nigeria. AIS tracking shows that it took two sharp turns off its course and slowed from 6.6 knots to a stop, before the signal ceased.
"It remains unclear what the current situation is with Stelios K," security company Dryad Global said. "Local authorities are currently investigating."
The tanker is owned by Royal Shipmanagement of the Marshall Islands, which could not be contacted.
On Tuesday morning, the 119,500-dwt SKS Donggang (built 2011) reported a suspicious approach 59 nautical miles south of Lome.
Dryad said a skiff with an unknown number of people on board came to within 0.5 nautical miles before it left.
The tanker changed direction slightly around the time of the incident and maintained speed, AIS data showed.
Heavy manoeuvres
Tommy Olofsen, executive chairman of the SKS Donggang's manager, OSM Maritime, told TradeWinds: "This was a suspicious approach and our emergency response system was activated immediately.
"Following use of best practice by our crew, including heavy manoeuvres, the suspicious vessel went away."
The crew members are safe and the company is in close contact with them.
This is the 10th incident in the Gulf of Guinea in November.
"As the rate of failed attacks increases, the perpetrators are highly likely to increase in desperation, both as a result of the increased risk to themselves from naval counter piracy activity, but from logistical strain also," said Dryad.
The company said the design of the tanker made it less vulnerable and probably discouraged an attempted attack.
"Vessels are advised to exercise heightened caution within and on approach to the Gulf of Guinea high risk area," Dryad added.
Five crew members were kidnapped in the Gulf of Guinea on Monday from the 1,700-dwt general cargoship AM Delta (built 1992) off Nigeria.
And on Friday, a gang kidnapped 14 Chinese crew members from a heavylift vessel. The 48,127-dwt Liberian-flagged Zhen Hua 7 (built 1998) was raided northwest of Sao Tome.
