Lagos - Nigeria must step up security for those displaced by Boko Haram violence, a global humanitarian agency said on Wednesday after suicide bombers killed 28 people at the entrance to a refugee camp."Camps sheltering innocent families fleeing war should be places of refuge. But instead they are turning into death traps," said a statement by Ernest Mutanga, head of the Norwegian Refugee Council (NRC) in Nigeria. "We need to see the Nigerian government stepping up to protect civilians in displacement camps. It's their primary responsibility."His remarks came after three female suicide bombers blew themselves up at the entrance to a camp for displaced people in Mandarari near Maiduguri in northeastern Borno state. Another 82 people were wounded."Camps like the one attacked yesterday sheltering displaced women and children are being indiscriminately targeted. Towns we previously considered safe for civilians are also under attack," Mutanga said. He said the insurgents had stepped up their attacks on "soft" targets, indicating there had been 190 security incidents involving civilians in the region last month - more than the total combined for May and June. There was also "an increase in the number of attacks on sites sheltering displaced civilians," he said. He said there had been two other attacks targeting the displaced in July which had killed eight people. "Armed groups in this conflict are pushing people from one hell into another."Rising insecurity was also hampering relief efforts in a region facing a dire humanitarian crisis. "Northeast Nigeria is already experiencing a widespread food crisis, with food security experts forecasting a rise in the number of people facing crisis, emergency and famine conditions from 4.7 million to 5.2 million by the end of the month," he said. The eight-year Boko Haram violence has killed at least 20 000 and forced some 2.6 million others to flee their homes.