Gunmen continue to battle government forces in violence in Nigeria''s southern oil region after the main militant group declared a state of war and raised the specter of a stepped-up conflict in Africa''s oil giant. Fighters riding in about 10 speedboats attacked security personnel guarding an oil-pumping station operated by Royal Dutch Shell PLC in a pre-dawn raid, touching off an hour long battle. The flow station may have been damaged during the battle, but no government forces were injured. Shell officials said they were investigating reports of attacks on their facilities but could give no further details. The Movement for the Emancipation of the Niger Delta, the region''s main militant group, claimed responsibility for the attack in a statement emailed to the media. Fighters stormed the facility and "razed it to the ground" killing workers and soldiers inside, the statement said. No casualty figures were given. Monday''s violence follows two other days of rare, deadly battles between the militants and Nigeria''s armed forces. The group has mostly focused on hobbling Nigeria''s oil industry since it emerged nearly three years ago, bombing pipelines in hopes of forcing the federal government to send more revenues to the impoverished oil-producing south. The militants, who analysts say are motivated by money as well as politics, say they want more federally held oil funds for their states, which remain impoverished despite five decades of production in Africa''s oil giant. Their attacks have cut about one-fifth of Nigeria''s normal oil output, helping send crude prices to all-time highs in international markets. The militants also said they blew up other pieces of oil infrastructure, but those claims couldn''t be immediately verified. The group warned international oil companies to stay away from the region. The militants said they had attacked a military outpost in recent weeks, killing 29 military personnel in response to alleged killings of civilians. The government denied that any attacks took place. The accounts could not be independently verified. Large-scale battles between the militants and military are rare. While the military often skirmishes with gunmen during chance boat encounters on the region''s waterways, it has avoided major attacks on militant camps and other permanent positions. The militants generally avoid the armed forces, sticking to the back creeks of the delta as they roam the region.