The International Maritime Organization (IMO) has expressed “deep concern” that two attacks on oil tankers in the Gulf of Guinea mark a resurgence of piracy in the area.

IMO Secretary General, Kitack Lim, said in a statement that he was “deeply concerned” over an attack involving the kidnapping of six crew members from the Monjasa Reformer and boarding of a second tanker, the Success 9.

Another tanker, the Success 9, was hijacked on 10 April around 300 nautical miles south-southwest of Abidjan, Côte d’Ivoire.

“There is 20 crew of various nationalities onboard the vessel, of which one of them is a Singapore citizen,” it said.

“Either a mothership was used to deploy a skiff, or a secondary tanker is in the vicinity to illegally offload the boarded vessel’s cargo,” Maritime security firm EOS Risk Group said in an alert.

It added that the two incidents “exemplified West African pirates’ ability to conduct piracy at great ranges from the shore”.

Lim said he appreciated the regional and international response to “this disturbing incident”.

“IMO urges continued sustainable support to the important work of the regional navies and entities within the Yaoundé Architecture to protect seafarers and to the operational piracy response from the Gulf of Guinea Maritime Collaboration Forum.”, Lim said.

But it added that more needed to be done to strengthen maritime security and tackle the root causes of piracy.

Martha Ama Akyaa Pobee, UN assistant Secretary-General for Africa, said at the time that piracy incidents were declining due to concerted efforts by national authorities but cautioned further work was needed to consolidate gains.

She estimated that the threat of piracy had cost the region over $1.9bn in financial losses every year.