The UN's emergency relief co-ordinator has cut short a visit to Somalia's capital amid fresh security concerns.
Mr Holmes cancelled plans for a second day in Somalia
John Holmes's arrival in Mogadishu coincided with several bomb blasts, one of which killed four people near the UN compound in the city.
He is the most senior UN official to visit the city in a decade, and was urging the Somali government to let humanitarian aid reach its people.
Two weeks ago the government declared victory over a bloody Islamic uprising.
"Mr Holmes returned to Nairobi today (Saturday) and plans for a second day in Somalia were cancelled," the UN humanitarian agency said in a statement.
'Responsibility to citizens'
Earlier, Mr Holmes called on the Somali government to look after its civilians, who have borne the brunt of years of fighting.
"It is their responsibility to look after civilians, to protect civilians and at the very least not to obstruct aid," he said.
He said the African Union could not boost its peacekeeping forces in the capital until the government improved security.
The capital has been mostly calm since the government declared victory over the insurgents and many residents are starting to return to their homes.
Some 1,600 people were killed in six weeks of clashes between Ethiopian government-backed troops and Islamist and clan fighters, local aid groups say.
Up to 400,000 of Mogadishu's 2m residents fled to squalid camps or makeshift bush shelters.
Somalia has not had a working government since a civil war erupted 16 years ago.