Lagos - Some 500,000 children have been forced to flee Boko Haram militants in the last five months after an upsurge in attacks in Nigeria, Cameroon, Chad and Niger, the UN children's agency said on Friday.
The additional numbers of children made homeless has taken the total number of youngsters in the Lake Chad region who have been forced to flee to 1.4 million, Unicef said in a statement.
Nigeria was worst affected, with nearly 1.2 million children - more than half of them under five - uprooted by the Islamist insurgency, which is concentrated in the country's remote northeast.
Some 265,000 other children have been affected in neighbouring Cameroon, Chad and Niger, which Boko Haram has increasingly targeted after they joined Nigeria's military in a regional counter-offensive.
"Each of these children running for their lives is a childhood cut short," said Unicef's regional director for West and Central Africa, Manuel Fontaine.
"It's truly alarming to see that children and women continue to be killed, abducted and used to carry bombs."
President Muhammadu Buhari has said he is confident "conventional" attacks will be stopped by November, although suicide and homemade bomb attacks could continue.
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Earlier this month, the International Organization for Migration revised upwards its estimate of those internally displaced by the conflict from 1.5 million to more than 2.1 million because of the recent surge in attacks.
The IOM's head of mission in Nigeria, Enira Krdzalic, said many IDPs living in host communities had yet to receive basic food and shelter, calling for more to be done.
On Wednesday, the charity Medecins Sans Frontieres also appealed for international help after 16 people died and 172 fell ill in a cholera outbreak at three IDP camps in Maiduguri, northeast Nigeria.
The UN regional humanitarian coordinator for the Sahel region Toby Lanzer, told AFP thousands of Nigerians who fled to a refugee camp in southeast Niger were in an "atrocious" situation.
Unicef said it had increased its operations in the Lake Chad region, including child vaccination programmes, education and psychological counselling.
Nearly 65,000 children under five had received treatment for severe acute malnutrition, it added.
But Fontaine said more funding was needed because the agency had only received a third of the $50.3 million required to finance its operations in the Lake Chad region this year.
That has left more than 124,000 children hit by the violence unvaccinated against measles. Some 208,000 are out of school and more than 83,000 lack access to safe drinking water.
"With more refugees and not enough resources, our ability to deliver lifesaving assistance on the ground is now seriously compromised," said Fontaine.
"Without additional support, hundreds of thousands of children in need will lack access to basic health care, safe drinking water and education."