The World Food Programme’s aid drop will be the first since the UN declared a famine in two areas of al-Shabaab controlled Somalia last week.
But the militants, who have links to al-Qaeda and banned the organisation from the country more than two years ago denied the claim, saying western aid agencies had a ‘hidden agenda’.
One of the worst droughts in 60 years is forcing thousands of Somalis to flee to Kenya for aid.
The situation is so desperate, said Josette Sheeran, head of the World Food Programme, that women are abandoning their dead children along the roadside.
Refugee routes into Kenya risk becoming ‘roads of death’, she said.
"We want to make sure the supplies are there along the road because some of them are becoming roads of death where mothers are having to abandon their children who are too weak to make it or who have died along the way," she said.
The United Nations also said it will start to airlift food aid into the Somali capital, Mogadishu, as well as eastern Ethiopia and northern Kenya today.
Speaking at emergency G20 talks yesterday in Rome, it said an extra £220 million is urgently needed to tackle the food crisis, which stretches across east Africa.
The number of Somalis needing urgent food aid has jumped by one million people and children are worst-hit, the UN's children's charity said. About 800,000 children there are now ‘acutely malnourished’ and need special feeding – an increase of 40 per cent. Eighty-two per cent of them are in the country's south, which is mostly cut off from aid deliveries.
Tomorrow, there will be another meeting in Kenya's capital, Nairobi, when fresh promises are expected to fund programmes to save up to 11.5 million people in the wider Horn of Africa region.
Some of the most vulnerable are seeking help in Mogadishu, Somalia's wrecked capital, which is struggling with more than 1,000 people pouring in a day.
Austin Kennan, from Irish aid organization Concern, which works in the region said he’d seen groups of exhausted families in the capital who had travelled for days or weeks, collapsed at the side of the road.
"At that stage, they're literally at the end of their tether," Kennan said. "The stories are actually what made it so horrendous, because every single family had lost two or more children,” he told CBS news.
"Often, it's women [walking] alone with children, so they're not even able to bury them properly; they just have to leave them and walk on, hoping that somebody else will bury them for them, which is absolutely traumatic."