UN chief Ban Ki-moon has warned that Somalia risks returning to famine without urgent aid.
His comments come as he visited the war-torn country three years since more than 250,000 people died of hunger.
"Over three million Somalis are in need of humanitarian assistance and unfortunately that number is growing," Mr Ban told reporters in the capital Mogadishu.
"I urge donors to step up contributions to avert another famine in Somalia."
The United Nations says it has just over a third of the cash it needs, having received $318 million of the $933 million it has appealed for.
Mr Ban, along with World Bank chief Jim Yong Kim, met Somali President Hassan Sheikh Mohamud inside the fortified airport zone, guarded by troops from the 22,000-strong UN-backed African Union force.
But Mr Ban said Somalia had made "remarkable progress" since he had last been there.
"Slowly but surely, Somalia is waking from a long nightmare," Mr Ban said.
However, he added that he was "very concerned" about the humanitarian crisis and the shortfall in funding.
Al-Qaeda-affiliated al-Shabaab insurgents have in recent months lost swathes of territory and towns to the AU force and Somali government troops, but they remain a potent threat.
This year they have launched attacks in the heart of Mogadishu, including brazen commando raids on the presidential palace and parliament.
Mr Ban, who said al-Shabaab's power "is declining but it is not gone", did not travel into the city itself, but remained inside the airport's concrete blast walls, manned by AU machine gunners.
The United Nations says over one million Somalis are in conditions close to famine.
Over one million have fled their homes due to fighting or hunger inside the country, and another million are living as refugees in the region.
About 218,000 children under five are acutely malnourished, a rise of 7% since the beginning of the year, the UN Office for the Coordination of Humanitarian Affairs (OCHA) has warned.
