Pirates who seized 15 Turkish sailors and killed one when they stormed a container ship in West Africa’s Gulf of Guinea at the weekend have not yet made contact with Turkish authorities for a ransom.

The Mozart was headed from Lagos to Cape Town sailing through the Gulf when armed seaborne attackers stormed it. Gulf waters border more than a dozen countries and is notorious for pirates raiding merchant vessels.

“We have not yet received word from the pirates,” Turkish foreign minister Mevlut Cavusoglu told reporters in Ankara on Monday. He said Turkey is also in touch with other regional African countries where the pirates may be holed up with their hostages.

Last year, pirates kidnapped 130 sailors in 22 incidents in the Gulf, accounting for all but five merchant seamen seized worldwide, according to an International Maritime Bureau (IMB) report.

The pirates come from Nigeria’s wild Niger Delta, experts say. The region produces most of the nation’s petroleum, but is underdeveloped with some of the highest unemployment in the country.

Gangs of men desperate for money engage in a variety of illegal activities, including kidnapping, stealing and refining oil, and piracy.

The IMB has tracked a steady increase in kidnappings over recent years, affecting everyone from fisherman to international supertanker crews.

Pirates who once stole cargo, or siphoned oil, discovered that some companies or even governments will pay large sums to ransom kidnapped crew.

Max Williams, chief compliance officer for security firm Africa Risk Compliance, told Reuters: “Saturday’s attack took place 200 nautical miles offshore, reflecting increasing sophistication, as vessels further from shore are less likely to have naval protection.”

Kidnapping and ransom insurance can cost shipping companies millions of dollars annually, though most refuse to discuss specifics due to fears it could make insured vessels a target.

Most countries in the region bar international navies or armed private security staff from their waters, but naval ships from France, Spain and Italy, already patrol the region’s international waters.

However, there is an urgent need for a coordinated international law enforcement operation, says Denmark’s Maersk, the world’s biggest container line.

“International mandates were found to secure the Hormuz Strait and the Indian Ocean,” said Aslak Ross, Maersk’s head of marine standards. “So we ought to be able to find a solution in West Africa.”