Militants battled security forces on Wednesday in two areas of Nigeria's oil-rich delta after armed men attacked a pumping station and an oil convoy, officials said.
A major militant group said in an e-mail they killed nine soldiers and captured two government gunboats at the pumping station belonging to a Royal Dutch Shell PLC subsidiary. The army gave no casualty figures and it was not possible to confirm the militants' claim.
The convoy -- attacked in a separate incident -- was carrying soldiers and supplies for Agip, a subsidiary of Italian oil company Eni SpA, Brigadier General Alfred Ilogho said. The convoy was on its way to an export terminal about 80km west of Nigeria's oil capital, Port Harcourt, Ilogho said.
Eni spokesman Gianni Di Giovanni said late on Wednesday that the company didn't have information about the attack. He added that Agip oil convoys are often local contractors.
"Attacks are frequent, and so is their lack of success. We must wait,"Di Giovanni said.
Chief Sara Igbe said militants attacked the pumping station in his community of Ekulama, about 40km west of Port Harcourt, sparking a battle with government forces. The Shell station pumps about 70,000 barrels a day.
"Youth from the community and the military resisted the attempts to shut down [the oil facility], and that's when shots were fired," Igbe said.
An e-mail from the Movement for the Emancipation of the Niger Delta -- a major militant group -- said they killed nine soldiers and captured two gunboats in an hour and half of fighting at the facility. The group said they acted defensively after being attacked by army gunboats and a helicopter gunship.
The militants said that they planned further attacks and warned oil companies to evacuate staff in the region.
"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," the e-mail said.
Witnesses said they saw government attack helicopters racing west from Port Harcourt toward the areas where the two attacks occurred.
The two attacks followed the release earlier on Wednesday of a group of Nigerians taken hostage on Monday. Biji Ojediran said that the last of the 25 hostage seized in a deadly raid on Monday were liberated overnight after nine had been set free earlier.
Gunmen also seized several foreign oil workers late on Tuesday, who remain in captivity according to security officials.
The British Foreign Office said four British oil workers were among those taken outside Port Harcourt. The workers were kidnapped from a residential compound close to Ekit, in Akwa Ibom state, it said.
Nigerian police spokesman Suur Chafa said a Romanian, an Indonesian and a Malaysian were also missing and believed taken hostage.