NAIROBI, Kenya — The United Nations is seeking $1.5 billion to fund hundreds of lifesaving projects in famine-struck Somalia next year, a top humanitarian official said Tuesday.

The 2012 appeal is based on realistic assessments of the emergency needs of four million people who are still in crisis months after famine was declared in July, said Mark Bowden, the U.N.'s humanitarian coordinator for Somalia. The funds will cover food, health and education projects.

"The Somalia crisis is everybody's responsibility and Somalis need support now," he said. "We can't afford to wait, or we will let down the Somali people."

He also called on all parties to Somalia's conflict to grant aid agencies unconditional access.

The Islamist fighters who rule much of the country's southern and central regions last month barred 16 aid groups from operating in areas under their control.

He said while the lives of tens of thousands of people were saved by the world's rapid response to the famine crisis, continued support is crucial to building the population's resistance to future drought and other shocks.

Bowden said the world's response to the famine has proven effective, with the number of people receiving food each month tripling to more than 2.6 million. He said more than 480,000 acutely malnourished children have received nutrition supplements, and that mass vaccination campaigns reduced cases of measles by almost 50 percent. Three of the six areas where famine was declared in July had improved to pre-famine levels by November, he said.

"Without the generosity of donors in providing emergency funds, tens of thousands more people would have died," Bowden said.

Somalia hasn't had a fully functioning government since 1991, when warlords toppled the country's last central government and plunged the Horn of Africa nation into a continuum of civil war, lawlessness and violence.