Hundreds of thousands of Somalis rely on food aid from the WFP
The UN's World Food Programme (WFP) has pulled out of large parts of southern Somalia because of threats from powerful Islamist rebel groups.
The WFP says the suspension is its biggest shut-down in years and will affect about one million people.
The al-Shabab militant group has repeatedly threatened the WFP - who it accuses of ruining local farming by forcing Somalis to rely on imports.
The WFP says without help, Somali farmers cannot supply enough food.
Drought and war have left more than 109,000 young children and many more adults dependent on the feeding centres run by the WFP.
But late last year al-Shabab, which controls large parts of southern Somalia, gave the WFP a deadline of 1 January to halt all of its operations in the area.
The group also issued a string of demands for aid agencies working in the region.
The WFP's Peter Smerdon said these included removing women from their jobs and a demand for a payment of $20,000 (£12,400) every six months for security.
"WFP's humanitarian operations in southern Somalia have been under escalating attacks from armed groups, leading to this partial suspension of humanitarian food distributions in much of southern Somalia," the agency said in a statement.
Six of its offices - in Wajid, Buale, Garbahare, Afmadow, Jilib and Belet Weyne - have been shut temporarily, which the agency said would affect more than a third of the people it feeds in Somalia, most of whom are women and children.
The WFP said it would continue food distribution in other parts of Somalia, including the capital Mogadishu.
Its staff who have been evacuated from the south will be redeployed in other parts of the country, preparing to help people who might start moving away from areas where feeding programmes have been suspended.
Somalia has been in turmoil since 1991 when its central government collapsed.
The transitional government, helped by an African Union peacekeeping force, runs only parts of Mogadishu.
Groups such as al-Shabab want to impose a hard-line interpretation of Islamic law on the country.