Pirates seized an oil tanker with over 20 crew off the coast of Nigeria, an official of the International Maritime Bureau said on Thursday amid mounting concern at such attacks in West Africa.

“We believe it’s been hijacked and we believe there are about 25 crew on board,” Cyrus Mody, a London-based manager with the world’s piracy watchdog told AFP on the phone.

The attack occurred on October 30, he said.

A Nigerian vessel servicing an international oil firm was also attacked on on the country’s waters off the Niger Delta region on Wednesday and its whereabouts were unclear on Thursday, a security source told AFP in the oil city of Port Harcourt.

Neither the nationalities of the crew on the tanker nor details of the vessel could be immediately confirmed. A Nigerian navy official was unable to confirm the incident.

The attacks are the latest in a surge of attacks along the Gulf of Guinea in recent months.

Twenty Eastern European crew hijacked off Nigeria last month were freed along with their vessel around a week later.

The coast of Nigeria, Africa’s largest oil producer, has long been a dangerous place to sail, and the risk has extended in recent months to the coast of the small neighbouring nation of Benin.

Benin’s coast has seen at least 20 piracy incidents this year compared to none in 2010. The two neighbours – Nigeria and Benin – in September launched joint sea patrols to tackle the piracy surge.

The maritime bureau has warned that the spate of attacks off West Africa indicates the region could emerge as a new piracy “hotspot”.

Unlike the explosion of piracy off the coast of Somalia on the eastern side of the continent in recent years, those involved in the recent west African attacks have so far not appeared to be after ransom payments.

Fuel or oil cargo has been stolen for sale on the region’s lucrative black market, while robberies have also occurred. Crew members have been beaten and the pirates tend to be heavily armed.

The theft of such cargo tends to be relatively sophisticated, with tankers often being directed to another pirate-controlled ship, where the fuel is siphoned and then taken elsewhere for sale.

Benin, Togo and Ghana will hold a meeting in Cotonou next week to hammer out ways to end piracy in the Gulf of Guinea.