Lagos - Two million people in need of assistance in the northeast of the country are cut off from help, the UN said on Tuesday, warning the scale of a food crisis could be worse than thought.
The UN children's agency UNICEF said on July 1 that 250,000 children under five in Borno state were at risk from severe acute malnutrition this year and 50,000 could die if nothing was done.
It repeated the warning Tuesday but said access to people in hard-to-reach areas was still limited, if not impossible, with the Islamist militants an ever-present danger.
"There are two million people we are still not able to reach in Borno state, which means the true scope of this crisis has yet to be revealed to the world," said Manuel Fontaine, UNICEF's regional director for Western and Central Africa.
"There are organisations on the ground doing great work but none of us is able to work at the scale and quality that we need. We must all scale up."
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Aid agencies have been warning for months that northeast Nigeria faces acute food shortages, after seven years of violence that has left at least 20,000 dead and made more than 2.6 million homeless.
Land in the mainly agricultural region, where already desperately poor people eke out a living from subsistence farming, has been devastated along with infrastructure, homes and businesses.
Concerns have been raised about high death rates from severe acute malnutrition in camps for the internally displaced, while it is feared some inaccessible areas could be suffering from famine.
The UN's regional humanitarian coordinator for the Sahel, Toby Lanzer, has compared the situation to crises in the Central African Republic, Darfur and South Sudan.
He disclosed on July 11 that "thousands of people will die" if nothing is done, and urged the international community to "step up" and provide funding.
A total of $220 million was needed for the next 10 weeks "for the purposes of keeping people alive", he said.
UNICEF appealed for $55.5 million earlier this year but said it has so far only received $23 million.