Nairobi/Abuja - A British citizen has been kidnapped in Nigeria's restive Niger Delta province as a militant group said it would release two South Africans kidnapped among a group of 27 others.

A spokesman for the Nigerian military in the Niger Delta Lieutenant-Colonel Musa Sagir said that the unidentified Briton was kidnapped late on Monday evening, but gave out no further details.

The news came as the Movement for the Emancipation of the Niger Delta (MEND), Nigeria's most prominent militant group, said it would release two South Africans captured along with 22 Nigerians, two Britons and another foreigner.

MEND said it had "rescued" the 27 from the group that had kidnapped them, but would hold them as hostages until one of its leaders, Henry Okah, was released from prison.

However, MEND said in a statement that Okah's wife, who lives in South Africa, had asked for the two to be released as South Africa had treated her with "respect and hospitality."

The release of the pair may be delayed, however, as MEND on Sunday declared an "oil war" and has since launched attacks on several pipelines and oil installations.

Militant groups such as MEND often attack oil installations and kidnap expatriate workers, saying they are fighting for a greater share of profits from oil exploitation for the poor of the region.

The government says they are merely criminal gangs intent on stealing oil and extorting money.

The unrest has cut oil production by around a fifth since early 2006, helping to push up global oil prices and allowing Angola to surpass Nigeria as Africa's biggest oil exporter. (dpa)