Piracy is common off Nigeria and often linked to militants
Pirates have seized a ship owned by a French company off the Nigerian coast, taking nine crew members hostage.
The company - Bourbon - said the captain had assured them that all crew members were unharmed.
Bourbon - which provides specialist boats for the oil and gas industry - said it was working to free the crew.
The hostages are from Nigeria, Ghana, Cameroon and Indonesia. Piracy is common in Nigerian waters, often linked to militants targeting oil companies.
Militants attack vessels and strip them of valuables, taking hostages for ransom.
The hostages are usually released later.
Rise in piracy
The Bourbon boat had left Bonny Island in the Niger Delta and was off the coast of Akwa-Ibom State when it was attacked.
Militants are holding two British hostages taken from another oil services vessel in September last year.
The Movement for the Emancipation of the Niger Delta (Mend) say they will only be released if one of their leaders, currently on trial, is freed.
Militants say they are fighting for a bigger share of the country's oil wealth, but many attacks are carried out by criminal gangs looking to extort money from oil companies, the government says.
Nigeria's oil production has been cut by around a fifth since 2006, partly as a result of the violence.
Boats in waters of neighbouring Cameroon have also been attacked.
The weekend attack comes as pirate hijackings increase, particularly in the waters off the coast of Somalia.
A French navy vessel captured 19 suspected pirates and foiled two attacks on Sunday targeting cargo ships in the Gulf of Aden.
In 2008, pirates attacked 111 ships off Somalia, hijacking 42 of them, and receiving tens of millions of dollars in ransoms.