Geneva - Violence by extremists has led to staggering levels of misery and hardship in the northeast, ranging from food shortages to families torn apart by relentless attacks, a top UN official said.
"We're seeing tremendous suffering," UN Assistant Secretary General Robert Piper told AFP in an interview this week.
The insurgency by Boko Haram militants, aiming to create a hardline Islamic state, has killed more than 13 000 people since 2009 and forced some 1.5 million others to flee their homes.
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The military, with help from troops from Chad, Cameroon and Niger, has claimed major gains against the Islamists in recent weeks, recapturing many towns held by the rebels.
But the impact of the fighting and violence has caused the humanitarian situation in the area to deteriorate rapidly over the past year, said Piper, who coordinates the UN's humanitarian work in Africa's Sahel region.
Surging food insecurity
The violence has among other things cut millions of households off from access to their farms, causing surging food insecurity.
"We estimate that only about 20 percent of agricultural land in Borno State (the hardest-hit area) was harvested last season," Piper said, pointing out that "that leaves a massive deficit."
At the same time, there are "dramatic rates of acute malnutrition" among the displaced children in Nigeria, he said.
A recent survey of displaced children around Maiduguri, the capital of the Borno State, showed more than 35 percent of them were acutely malnourished, Piper said, stressing that that is "very, very high."
But even as the humanitarian needs balloon, the security situation is making it far more difficult for aid workers to get in.
"We've had to pull back because of fighting," Piper lamented, acknowledging that large parts of northeastern Nigeria and even areas in neighbouring countries hosting Nigerian refugees were out of reach.
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"It is simply too dangerous," he said, adding that the UN in the next couple of weeks hoped to establish a "humanitarian air corridor" to make it easier and safer to move aid workers in and out of the northeast.
The violence wracking Africa's most populous country is meanwhile sending shockwaves through the entire region.
Militants have been increasingly carrying out cross-border attacks into Cameroon, Niger and Chad, which are also struggling to host around 200,000 Nigerian refugees, Piper said.
In addition, around 100 000 Cameroonians have been displaced further inland to get away from the volatile border areas.
Piper said he and other humanitarians were "absolutely horrified" at the stories they were hearing from the Nigerians uprooted from their homes.
He said he had spoken with people displaced in Adamawa state and was "struck by the complete absence of men, husbands and even young boys in these families."
"Without exception, they had all been killed," he said, adding that most of those forced to flee had lived through "staggering trauma".
In Niger, the world's poorest country, he had visited houses that once housed 10 people and now counted 30, after taking in refugees.
"The generosity of these communities is breathtaking," he said.
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The needs are staggering.
Piper says a "fairly conservative estimate" is that Nigeria is facing "a $1.0-billion humanitarian crisis" this year alone.
The government will have to foot most of that bill, he said, but the UN's humanitarian agency is asking donors to cough up $100 million for its 2015 operations in the country.
Even though the amount is relatively small, Piper acknowledged "it's going to be a great struggle to raise."
Nigeria, Africa's largest oil producer, is generally perceived as relatively prosperous, and it is hard to raise funds for, he said.
Last year, the agency received just 18 percent of the $93 million requested for the country.
"It's impossible to imagine us responding to the scale of today's crisis if we have a repeat of 2014 on the funding side," Piper said.
"We may as well pack up and go home."
UN humanitarian chief Valerie Amos announced late Thursday the UN would release $28 million from its central emergency response fund to help those fleeing the violence in Nigeria.