On a street by the river port in the oil town of Warri, dozens of Nigerian soldiers and marines shelter behind sandbags, pointing their machine guns towards an unseen enemy. They are mounting a 24-hour watch on the southern approaches of the Warri River. "The situation in the Niger Delta has graduated from restiveness to insurrection," Enilama Umoku, a political science lecturer at Delta State University near Warri, told IRIN.