The nationalities of those taken was not immediately known.

Series of kidnappings

In an earlier attack, armed men took 11 Russians and a Ukrainian on a vessel off Bonny late on Thursday.

Some were released on Friday, but five were still being held, security officials said.

More than a dozen men in speedboats kidnapped two oil engineers, one from the Philippines and one Nigerian, from a vessel in the main industry hub of Port Harcourt on Friday.

Another Filipino was seized while on land.

Security sources said it was not clear whether the same group was behind all the kidnappings.

No ransom demands have yet been publicly made.

Groups aruging that Nigerians are not benefitting from the wealth of local resources make frequent attacks on installations in their campaign.