OSLO: Shipping company Trico Marine Services said on Wednesday four foreign workers were kidnapped from one of its supply vessels off Nigeria. The head of Trico Marine's Norwegian subsidiary told Reuters that two Norwegians and two Ukrainians were abducted. "We will not come out with more information than that four of our crew were taken from a ship off Nigeria," Managing Director Bjoern Endresen told Reuters. He said no demands had been made and did not specify where the ship was located expect to say it was in Nigerian territorial waters when the kidnapping occurred. Kidnappings of foreign workers are frequent in Nigeria, especially in the Niger Delta. Militant attacks on western firms are fuelled by widespread feelings of injustice in an oil-rich country where most people live in poverty. Criminal gangs have also been involved in kidnappings for ransom. Hostages are usually released unharmed after a few days when a ransom has been paid, which analysts say fuels the violence. Nigeria is the world's eighth largest oil exporter and the largest in Africa.