The British Foreign Office said on Friday that seven oil workers have been abducted in Nigeria.
A Briton, two Colombians and an Australian were confirmed to be among the hostages, and the Foreign Office said a Russian was also believed abducted.
It was not yet clear who kidnapped them, the department said. But hostage-takings are common in Nigeria's oil delta, where activists and thugs frequently target oil companies with sabotage, kidnappings and other attacks in a bid to extort payoffs. The hostages are rarely harmed.
The British worker, whose identity was not released, was kidnapped on Thursday in the southeastern Warri region of the country where he worked for a firm that contracted staff to oil companies, a Foreign Office spokesman said.
"We can confirm that a British national was abducted on Nov. 27 along with a number of his colleagues of various nationalities in the Warri area of Nigeria," the spokesman said.
"It is still unclear who they would have been abducted by. We are speaking to local authorities to find out what has happened and who the perpetrators were," he said.
Bredero Shaw, a pipeline coating company for which at least three of the victims reportedly worked, said the kidnapping had taken place as the workers tested an evacuation boat on the river behind the plant.
No details were available of exactly what happened.
Colombia said two of its nationals, both of whom worked for Bredero Shaw, were kidnapped, and Australia confirmed a 27-year-old Australian was among those seized. Britain said a Russian was believed to have been abducted.
The British man also reportedly worked for Bredero Shaw.
Bredero Shaw's safety manager Ted Scheffey said one of the hostages had been freed, but did not identify him by name or nationality.
"Communications are currently under way between the captors and the Nigerian officials to secure the release of the others," he said.
In the summer, at least five oil workers, including a Briton, were kidnapped in a month in the volatile petroleum-rich delta region. They were freed without any ransom paid.