Kidnappers in Nigeria have attacked a Shell-operated oil facility in the Niger Delta, killing at least five soldiers and taking five foreigners hostage. It comes amid rising militancy in the impoverished area, just days after eight foreign oil employees were taken hostage and then released at the weekend. Security incidents so far this year have shut down a quarter of oil output from OPEC member Nigeria, the world’s eighth-biggest crude exporter. Violence in the Delta has complex causes. Most of the inhabitants are poor and have seen few benefits from the region’s oil riches, while extraction work has polluted their air and water. A coalition of three groups has claimed responsibility for today’s attack, which, it says, was in response to a court decision to deny bail to a jailed militant leader.