The main militant group in Nigeria's oil-producing Niger Delta region
says it has attacked the Royal Dutch Shell Utorogu gas plant.
In a statement, the Movement for the Emancipation of the Niger Delta (MEND) says it attacked the plant early Saturday to dispel any false sense of security in the region.
Nigerian officials have confirmed the attack, but say the rebels were repelled and three of the attackers were killed. MEND denies any of its members were killed.
Meanwhile, the militants also issued a separate statement Saturday confirming they had released the wife of Nigeria's former energy minister, Edmund Dakouru. She had been kidnapped earlier in the week.
The militants say $2.5 million was paid for her release, but that ransom could not be confirmed.
On Friday the group said a British hostage they are holding is very ill and they contacted a doctor to examine him.
Kidnappings and other attacks are common in the restive, oil producing region. Militants say they are fighting for a better redistribution of wealth in the impoverished area.
Earlier Friday, it was reported that a Nigerian boy who had been kidnapped in the region last week had been released unharmed. His sister was killed trying to prevent the kidnapping.
The father of the children also works for Royal Dutch Shell. The identity of the gunmen and kidnappers is not yet known.
Militants, some of them linked to corrupt government officials, have been kidnapping oil workers and their families for many years in the Niger Delta to get ransom money or protection contracts.
Some information for this report was provided by AFP, AP and Reuters.