LAGOS: Armed pirates who stormed an oil service ship off Nigeria have kidnapped six foreigners and demanded a $US1.3 million ($1.26 million) ransom for their release, the police and military say.
"Three of those abducted are from Ukraine, two from India, one from Russia," Bayelsa state police spokesman Fidelis Odunna said of the Sunday attack.
Ukraine's Foreign Ministry however issued a statement saying its three nationals had already been released, but it provided no details regarding the circumstances and Nigerian security officials were not available to confirm the development.
"According to the embassy of Ukraine in Nigeria, the three kidnapped Ukrainians... have been released. Their life and health are not in danger," the statement said.
The kidnapping of foreign oil workers is common in Nigeria's oil-rich south, with the hostages often released following a ransom payment. It is however rare for police to discuss the details of ransom demands.
There has also been a recent series of kidnappings in northern Nigeria claimed by an extremist Islamist group, but those are considered a different phenomenon.
The Armada Tuah vessel operated by the Lagos-based Century Group with a crew of 15 was attacked by gunmen 40 nautical miles off southern Bayelsa state at about 2am AEDT, the area's military spokesman, Colonel Nwachukwu Onyema told AFP.
The vessel was en route from the oil-hub of Port Harcourt to Abo, the site of a key deepwater oil field, where Shell, Italy's Agip and several domestic firms have operations, Onyema further said.
The International Maritime Bureau which tracks sea attacks world-wide has described the waters off Nigeria as an emerging piracy hub, with many of the raids involving gunfire.
Militants in Nigeria's oil-producing Niger Delta region carried out scores of kidnappings before a 2009 amnesty deal led to a sharp decline in unrest, though incidents continue.
Five Indian crew members of an oil tanker who were kidnapped in December after heavily armed pirates stormed their vessel off Nigeria's coast were released last month.
Medallion Marine, a Mumbai-based shipping firm, said the hostages were freed in good health, but did not disclose whether a ransom had been paid, or whether Nigeria's security forces played any role in securing their release.
The theft of crude is considered a key motivation for pirates operating in the Niger Delta.
Armed gangs in the region have become notorious for blasting into pipelines and siphoning out crude for sale on the lucrative black market.
Oil Minister Diezani Alison-Madueke on Tuesday told an oil industry conference in Abuja that Nigeria was seeking international help to curb criminality in the region.
Meanwhile in a separate abduction case, a French family of seven kidnapped in northern Cameroon on Tuesday were believed to have been taken across the Nigerian border, Yaounde said, suggesting the hostage-takers may be linked to Nigeria's main Islamist insurgent group Boko Haram.
Nigeria is Africa's biggest oil producer and most populous country with an estimated 160 million people, where most in the north are Muslim while the south is predominantly Christian.