Six separate hijackings of coastal tankers in order to steal the cargo have occurred since April, the IMB says.
It explains the incidents mark a shift from the previous pirate preference in the area to target ships at anchor.
Pottengal Mukundan, IMB Director, said: “The recent increase in the number of successful hijackings is a cause for concern.
“These serious attacks have so far targeted small coastal tankers. We advise these vessels to maintain strict anti-piracy measures in these waters, and to report all attacks and suspicious approaches by small craft.”
Mukundan’s caution came as the IMB revealed piracy has experienced a further downturn in the opening half of 2014.
The IMB counts 116 incidents in the six months to the end of June, down from 138 in the same stretch of 2013.
This year has seen 10 first half hijackings, 78 ships being boarded and 21 reported attacks.
“Two hundred crewmembers were taken hostage, five kidnapped from their vessels and there were two fatalities,” the IMB said.
Only 10 incidents were noted off the previous hotbed of Somalia, with three ships being fired upon.
Mukundan warned: “While we welcome the continued decline in the number of Somali incidents the risk of piracy has not completely diminished. Ship masters are reminded to remain vigilant and apply the Best Management Practices guidelines.”
West Africa witnessed 23 incidents and six hijackings in the first half of this year, the report said, noting Gulf of Guinea piracy was particularly violent.
Indonesia was another hot spot with 47 incidents, including 40 in which vessels were boarded.
