A Nigerian armed militant group in the oil-rich Niger Delta said it had killed nine soldiers in a firefight in the restive region.
"In the ensuing firefight, which lasted about one and a half hours, our units captured two gunboats, killing all occupants, nine soldiers," the Movement for the Emancipation of Niger Delta (MEND) said in a statement emailed to the agency.
There is yet no official confirmation of the MEND's statement.
MEND said that at about 5 pm (2130 IST) on Wednesday, its units dispatched to communities in Rivers State were attacked by nine gunboats and one helicopter gunship of the Nigerian Army.
"Our presence in Rivers State is being beefed up by about 500 fighters which had earlier been dispatched and will be in Rivers State by nightfall," the MEND statement said.
The group said that it was being "forced" to act ahead of its planned major strike on the nation's oil industry.
It warned operators of oil facilities in Rivers State to immediately evacuate their workers from such locations, adding that it will not change its decision not to take hostages in attacks on oil installations.
Rather, "we will commence with a number of strategic attacks on targets of relevance. This will commence with effect from today and will increase in severity depending on the response from the Nigerian military," it concluded.
On Monday, about 70 armed men attacked a site belonging to the Royal Dutch Shell company in Rivers State, killing 14 soldiers and kidnapping 25 workers, who were later released, military and company sources said.
Seven expatriate workers were kidnapped late on Tuesday by an armed group in the region.