Lagos, Dec 4 : The office of the UN High Commissioner for Refugees (UNHCR) said repeated attacks in northwest Nigeria forced over 11,500 Nigerians to flee across the border to neighbouring Niger in November, resulting in a humanitarian crisis. In recent weeks armed groups, locally called "bandits", have repeatedly attacked villages in northwest Nigeria. The violence comes against the backdrop of inter-communal clashes between farmers and herders as competition increases for dwindling resources, aggravated by the climate crisis, said a UNHCR statement reaching Xinhua on Friday. "We are deeply concerned by the surging violence in northwest Nigeria and call for concerted and massive support to address the growing humanitarian needs of the affected population, ranging from protection services to food, shelter kits, kitchen utensils, blankets, and other non-food items," said the statement. It said most of the November arrivals from Nigeria have taken shelter in rural communities in Niger's Tahoua region, which was already hosting 3,500 Nigerian refugees since September, Xinhua news agency reported. Women and children make up most of the recent arrivals and describe killings, kidnappings for ransom and the looting of their villages, UNHCR said. The UN refugee agency is registering new arrivals, providing emergency help and identifying the most vulnerable in coordination with Nigerian authorities, said the statement. "But the need for shelter, food, water, and healthcare is rising rapidly," it said, calling for expanding support from the international community. Armed banditry has been a primary security threat in Nigeria's northern and central regions, leading to deaths and kidnappings in recent months. /IANS