MOGADISHU, Somalia (AP) -- A plane carrying 10 tons of urgently needed nutritional supplements to treat malnourished children has landed in famine-hit Somalia, a U.N. official said Wednesday.

The airlift is part of a crisis intervention as famine threatens to spread across lawless Somalia.

David Orr, a World Food Program spokesman who flew with the shipment from neighboring Kenya to the Somali capital of Mogadishu, said it was the first airlift of food aid since the U.N. declared a famine in parts of Somalia last week.

Orr said the aid would be distributed to medical facilities to treat the malnourished children.

WFP spokeswoman Challiss McDonough said this is first of several planned airlifts in coming weeks. She said Wednesday's shipment of peanut butter-based nutritional paste will treat 3,500 malnourished children for one month.

McDonough said WFP decided to send in the airlift because of an urgent need to treat the growing number of internally displaced children suffering from malnutrition before their condition deteriorates.

She said about 18,000 children are suffering from malnutrition and that the number is expected to grow to 25,000.

WFP says it cannot reach 2.2 million people in need of aid in the militant-controlled areas in southern Somalia because of insecurity.

Somalia has been embroiled in conflict for two decades, since the last leader was overthrown by warlords who then turned on each other. Islamist militant groups have spent the last few years battling the weak U.N.-backed government in an attempt to overthrow it.

Al-Shabab - the most dangerous militant group in Somalia - said last week it will not allow the aid groups to operate in its territories, exacerbating the drought crisis.

Earlier this month al-Shabab, which has links to al-Qaida, had shown indications of wavering on its 2009 ban on certain aid groups in its territories.

The drought has created a triangle of hunger where the borders of Ethiopia, Kenya and Somalia meet. WFP estimates more than 11.3 million people need aid across drought-hit regions in East Africa. The majority of those affected live in pastoral communities whose herds have been wiped out because of a lack of water.

Separately, UNICEF said Wednesday that it is trying to vaccinate more than 300,000 children in Kenya in an emergency program designed to prevent an outbreak of disease as refugees stream into northern Kenya.

Jayne Kariuki from UNICEF said that four northern Kenyan regions will be targeted along with Dadaab, the world's largest refugee camp, during the two-week program to immunize the children against polio and measles.

The children will also receive vitamin A and de-worming tablets. In Liboi, a dusty town in Kenya near the border with Somalia, mothers in long robes clustered around with children as aid workers dispensed medicine under a thorn tree.

Kenya recorded it first polio case infection in 20 years in 2009, after a four-year-old girl was diagnosed with the disease along the country's remote border with Sudan.

Polio is an infectious disease that mainly strikes children under five. It causes paralysis and can be fatal.

In 2006, two refugees escaping the war in Somalia were diagnosed with the disease at the Dadaab refugee camp at Kenya's eastern border with Somalia. That outbreak was contained before it spread.

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Associated Press writers Tom Odula in Nairobi, Kenya and Katharine Houreld in Liboi contributed to this report.

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