Mukundan said ships must report all attacks and suspicious approaches
The International Maritime Bureau (IMB) says the rise in piracy in Southeast Asia could represents a new trend, Platts reports.
The region has suffered the majority of attacks in the world so far this year, with at least six cases of coastal tankers being hijacked for their cargos since April.
Previously most attacks were on vessels at anchorage, which were only targeted for petty theft.
"The recent increase in the number of successful hijackings is a cause for concern," said IMB Director Pottengal Mukundan.
He said ships must report all attacks and suspicious approaches by small boats.
Pottengal Mukundan, Director, IMB
The recent increase in the number of successful hijackings is a cause for concern
Overall, piracy and armed robbery incidents fell to 116 in the first half of 2014 from 138 in the same period last year, but Indonesia, Malaysia, Singapore Straits, Bangladesh, and Nigeria accounted for 70 percent of all attacks this year.
Only 10 incidents occurred near Somalia, formerly a major piracy hot spot, so far this year.
"We welcome the continued decline in the number of Somali incidents [but] the risk of piracy has not completely diminished," Mukundan said.
German insurer Allianz warned earlier this month that the rise in attacks around Indonesia could suggest "a potential for such attacks to escalate into a more organized piracy model unless they are controlled."