Mohamud Sakow, local head of U.S.-based Mercy Corps charity, was attacked while walking to his house in Jamame town, north of rebel-held Kismayu port, on Saturday night.
"Men armed with pistols shot him in the head and he died on the spot," resident Hussein Ali told Reuters by phone.
"We do not know who killed him and why. Mercy Corps was running many feeding centres and clinics in the area."
Assassinations, kidnappings and attacks on aid workers have been rife this year amid the chaos of an Islamist insurgency against the government and its Ethiopian military allies.
Gunmen stormed an airstrip in central Somalia earlier in the week, kidnapping two Kenyan pilots and four European aid workers. They were taken to Mogadishu, locals said.
Suspicion for attacks generally falls on clan militia or Islamist militants, though rebel leaders have said the government is behind the killings to discredit them and stir the international community into an intervention.
Fighting has rumbled in Mogadishu in recent days, with at least six civilians dead and 10 others wounded from Islamist attacks on Ethiopian and government bases, locals say.
(Writing by Abdi Sheikh; Editing by Andrew Cawthorne)
- Reuters - Thomson Reuters Foundation
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