BonnyIsland, in the southern Niger Delta, is home to a liquified natural gasterminal whose exports account for 10 percent of world supply and toNigeria's biggest crude-oil export facility.
This makes the heavily-guarded facility a prime target for militants out to sabotage the oil industry.
Thearmy says it recovered weapons and ammunition from the gunmen who hadcome in six boats to attack navy vessels and military personnelpatrolling the export facility.
The attack was the first majorstrike by militants in the restive oil-rich region since the country'smost prominent armed group, the Movement for the Emancipation of theNiger Delta, declared a ceasefire last month.
Daniel Ebahor, ofthe non-governmental group Niger Delta Peace Foundation, says thegovernment's inability to take full advantage of the truce isresponsible for the resurgence of violence.
"I do not know whatthe government is doing. Government is not helping matters about theNiger Delta issue and there is no clear picture of the government'sability to restore peace in the region," he said.
There has beenviolent unrest in the Niger Delta region, where militants havekidnapped more than 250 local and foreign workers and damaged severaloil and gas pipelines and other facilities.
Armed groups in the region are calling for a more equitable distribution of the country's oil wealth.
Nigeria is the world's eighth-largest oil exporter, but militant raids have cut shipments by a fifth.