The World Food Programme is stepping up its aid effort to Sudan's troubled Darfur region, airlifting almost 100 extra tons of food a day.
Food is badly needed in Darfur
The push comes at what the WFP says is a critical stage, when the "rainy season begins to bite", making aid deliveries much harder.
The UN said there are now nearly 1.5 million people in need of help.
Most of them have left their homes in Darfur to flee Arab militias, accused by many of atrocities.
Sudan has two weeks to rein in the militias or face UN sanctions.
The Sudan government denies backing the Arab Janjaweed militias and blames two Darfur rebel groups for the humanitarian crisis, for taking up arms 18 months ago.
The WFP says that if the sand and gravel runway at El Geneina, the capital of the West Darfur region, becomes unusable because of the rains, any food that remains undelivered will be air-dropped directly to the town from two Ilyushin-76 planes.
"Delivering food by air is an expensive option but at this time of the year we have no other choice in parts of Darfur," said WFP Sudan Country Director Ramiro Lopes da Silva.
More than 1m displaced
Up to 50,000 killed
More at risk from disease and starvation
Arab militias accused of ethnic cleansing
Sudan blames rebels for starting conflict
In addition to the nine daily flights by three Antonov-12 aircraft, 21 trucks are due to leave the capital, Khartoum, with more food for El Geneina.
A UN spokesman said the number of internally displaced people in the Darfur region had increased to 1.2 million, from the one million reported last month.
In addition, there are 270,000 people in need of humanitarian assistance, "bringing the total number of conflict-affected people in Darfur to a staggering 1.48 million people," Radhia Achouri said.
Meanwhile, the UN's senior envoy to Darfur has called for thousands of observers and troops to be sent to the remote region the size of France.
Jan Pronk told London's Financial Times newspaper that the African Union force which has started to arrive in Sudan was too small.
Some 150 Rwandan troops landed last week and Nigeria's President Olusegun Obasanjo has asked parliament to approve the deployment of between 150 and 1,500 Nigerian troops.
On Tuesday, the Sudanese authorities allowed aid deliveries into a camp for 90,000 internally displaced people in Southern Darfur for the first time in three days.
Kalma camp near Nyala was closed last week, denying access to aid workers and United Nations staff, following riots in which one Arab refugee suspected of belonging to the Janjaweed militia was killed.