Sean Devereux, 28, was the first foreigner to be killed by gunmen since United States-led forces arrived in Somalia on 9 December. He was the Unicef officer in charge in Kismayu.
A Unicef statement said: 'We at Unicef Somalia . . . are stunned and deeply saddened by the death of Sean. Our deepest condolences go out to his family and friends around the world.' A Unicef spokesman in New York said Mr Devereux was shot in the back of the head while he was walking away from a Unicef office.
Mr Devereux, from Camberley, Surrey, was evacuated from Kismayu after an orgy of killing in the city that began on 8 December. He returned to his post shortly before the arrival of US and Belgian troops on 20 December. He had worked for Unicef in Somalia since last September.
News media widely quoted Mr Devereux's reports that the 8 December deaths were 'targeted clan killings'. Other reports, quoting diplomats and Kismayu residents, have since said 100 prominent members of the Harti clan in the town were systematically taken from their homes and shot by fighters of the Ogadeni clan warlord, Colonel Omar Jess.
Mr Devereux was killed on the eve of a three-hour visit to Mogadishu by the UN Secretary-General, Boutros Boutros-Ghali.