Up to 500,000 people in Kenya will need humanitarian assistance in the weeks ahead if the country's political crisis intensifies, the UN has warned.
The UN says half a million Kenyans urgently need help
The UN Office for the Co-ordination of Humanitarian Affairs said 255,000 had been forced from their homes and that malnutrition was now a growing risk.
Earlier, the main opposition party said it would resume its nationwide campaign of mass demonstrations next week.
Kenyan police said they would not allow the three days of protests to go ahead.
Some 600 people have been killed in the ethnic and political unrest sparked by the announcement of Mwai Kibaki's re-election as president on 27 December.
The defeated presidential candidate of the Orange Democratic Movement (ODM), Raila Odinga, has accused Mr Kibaki of rigging the poll and that his government has no interest in dialogue or mediation.
The former UN Secretary General, Kofi Annan, who is leading a panel of African mediators attempting to resolve the crisis, has meanwhile appealed to all sides for restraint.
Mr Annan called on "all Kenyan leaders, government as well as the opposition in the country to avoid any measures or steps that would further compromise, the search for an amicable solution to the country's crisis" in a statement issued on Friday.
Talks conducted by the chairman of the African Union, Ghanaian President John Kufuor, broke down on Thursday.
At a news conference in Geneva, a spokeswoman for the UN Office for the Co-ordination of Humanitarian Affairs said that 255,000 people had been forced from their homes by recent political upheaval in Kenya.
"OCHA estimates that nearly half a million people will need assistance in the coming weeks and months," Elisabeth Byrs said.
"It's anticipated that malnutrition will rapidly worsen if insecurity and lack of access to food and assistance persists," along with the destruction of farms and family livelihoods, she added.
The UN children's agency, Unicef, also said it was concerned about malnutrition, which already affected one in three children under the age of five before the crisis.
With hundreds of thousands of displaced people with no jobs or income, the situation for many children could become critical, it warned.
Food prices are also rising in the poorer suburbs of Nairobi, where many people have lost their jobs in the wake of the recent violence and goods are scarce.
The UN World Food Programme (WFP) has begun distributing food to 33,000 people around Nairobi, but it remains concerned that the situation will remain extremely volatile as long as the political crisis continues.
The OCHA said $7m had been granted by the UN's Central Emergency Response Fund (CERF) to help agencies fund their operations in Kenya and an emergency appeal for more would be launched next week in New York.
Meanwhile in Geneva, Unicef published accounts gathered by its staff in Kenya from children and young people who witnessed the violence.
Many described how the children were forced to watch their parents being attacked or killed, their homes burning, and their friends from different ethnic groups becoming enemies.